JP2010254545A - Silicon nitride-based composite ceramic and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon nitride-based composite ceramic which has high strength and also has excellent thermal shock resistance. <P>SOLUTION: The composite ceramic comprises a silicon nitride-based ceramic as a matrix phase and, combined therewith, boron nitride as a dispersed phase, the proportion of the boron nitride being 2.5 to 10 vol.%. When the four-point bending strength as measured at 25°C in accordance with JIS R1601 is expressed by σ<SB>i</SB>and the four-point bending strength as measured after a thermal shock is applied thereto by quenching from 800°C or higher through dropping into 25°C water by the dropping-into-water method according to JIS R1615 is expressed by σ<SB>f</SB>, then the value of σ<SB>i</SB>is 400 MPa or higher and the ratio of σ<SB>f</SB>/σ<SB>i</SB>is 0.85 or higher. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a silicon nitride-based composite ceramic suitable as a cast member made of aluminum, magnesium, or the like, and a method for producing the same.

  Silicon nitride ceramics are applied in many industrial fields because of their high strength, high hardness, heat resistance, and corrosion resistance. In addition, in order to improve the thermal shock resistance of silicon nitride ceramics, a composite with boron nitride has been attempted. However, since boron nitride has poor wettability with the silicon nitride glass component, when a large amount of boron nitride is added, the sinterability is lowered, and it is difficult to obtain a dense material having high strength. In addition, normal hexagonal boron nitride (h-BN) has a plate-like crystal form, and when dispersed in a silicon nitride sintered body, the shape of boron nitride becomes acute and acts as a defect. There has been a problem of lowering. Therefore, efforts have been made to solve these problems.

  For example, for the purpose of improving thermal shock resistance, a mixture of silicon nitride powder and boron nitride powder is added and mixed with β sialon powder, aluminum nitride powder and rare earth element oxide powder as sintering aids, respectively. Thereafter, a method for producing a composite ceramic to be sintered has been proposed (see Patent Document 1). In this manufacturing method, silicon nitride powder and boron nitride powder are mixed in a weight ratio of 90:10 to 70:30.

  Apart from this technique, a silicon nitride-based composite material in which fine hexagonal boron nitride is uniformly dispersed in the crystal grains and / or grain boundaries of the silicon nitride matrix has also been proposed (see Patent Document 2). In this composite material, the content ratio of hexagonal boron nitride is 1 to 25 vol. %It has become. The same document describes that by adopting this configuration, the composite material is greatly improved in mechanical strength such as fracture strength and thermal shock resistance.

JP-A-6-1003009 JP-A-9-169575

  However, in the technique described in Patent Document 1, hexagonal boron nitride, which is a normal plate crystal, is added, so that the boron nitride inside the sintered body has a large aspect ratio, resulting in a fracture source. Will act as. As a result, the strength of the composite ceramic is reduced.

  In the technique described in Patent Document 2, urea and boric acid are used at the time of production, and hydrogen treatment is necessary, so the process becomes complicated. Moreover, not only are facilities limited, but they can be dangerous. Furthermore, the literature discloses that the content ratio of hexagonal boron nitride is 1 to 25 vol. %, The lower limit of the ratio described as a specific example is 5 vol. %, And 5 vol. No specific effect has been confirmed in the case of less than%. Moreover, although the document describes the effect on thermal shock resistance, the effect is not specifically illustrated.

  Accordingly, an object of the present invention is to provide a silicon nitride-based composite ceramic that can eliminate the various disadvantages of the prior art described above.

The present invention uses a silicon nitride-based ceramic as a parent phase, and boron nitride is 2.5 vol. % Or more, 10 vol. % As a dispersed phase at a ratio of
Four point bending strength after giving thermal shock in quenching due put into water of 25 ° C. from 800 ° C. or higher by the water dropping method the four-point flexural strength in compliance with σ _i, JIS R1615 at 25 ° C. conforming to JIS R1601 when was the sigma _f, in which the value of sigma _i is greater than or equal to 400 MPa, and the value of the ratio of σ _f / σ _i is to provide a composite ceramic, characterized in that at least 0.85.

Further, the present invention provides a suitable method for producing the above composite ceramics,
Including mixing and forming a silicon nitride-based ceramic raw material powder that forms a parent phase and a boron nitride raw material powder that forms a dispersed phase, and firing.
As boron nitride raw material powder, t = 0.9λ / (Bcos θ _B ) (where, λ represents the wavelength (nm) of the X-ray tube, B represents the half width (rad), and θ _B represents the diffraction angle ( The present invention provides a method for producing a composite ceramic, characterized by using a crystallite size defined by rad) of 40 nm or more and less than 48 nm.

  ADVANTAGE OF THE INVENTION According to this invention, the silicon nitride group composite ceramics which are high intensity | strength both in room temperature and high temperature, and were excellent in the thermal shock resistance and oxidation resistance are provided.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The composite ceramic of the present invention is made of a silicon nitride-based ceramic as a parent phase. This matrix is generally composed of β-silicon nitride. And in this mother phase, boron nitride is compounded as a dispersed phase. By compounding boron nitride as a dispersed phase in silicon nitride, which is the parent phase, the strength, thermal shock resistance and acid resistance at room temperature and high temperature (for example, 600 to 1400 ° C.) compared to the case of silicon nitride alone. Improves conversion.

  Boron nitride as a dispersed phase is 2.5 vol. % Or more, 10 vol. % Or less in a generally uniform and fine state. The ratio of boron nitride is 2.5 vol. If it is less than%, boron nitride is not uniformly dispersed throughout the composite ceramic, and the thermal shock resistance is not improved. Conversely, 10 vol. If it exceeds 50%, the sinterability of silicon nitride decreases and the fracture strength decreases. From the viewpoint of obtaining a composite ceramic having higher strength and excellent thermal shock resistance, the ratio of boron nitride to the entire composite ceramic is 2.5 vol. % Or more, 5 vol. % Or less is preferable. The proportion of boron nitride in the composite ceramic can be measured by X-ray diffraction, wavelength dispersion elemental analysis, or the like.

As described above, the composite ceramic of the present invention has high strength and excellent thermal shock resistance. In general, the strength of a ceramic material is evaluated by a four-point bending strength according to JIS R1601, and the composite ceramic of the present invention has a four-point bending strength σ _i of 400 MPa or more at room temperature, for example, at 25 ° C. Preferably, it exhibits a very high value of 500 MPa or more and 900 MPa or less, more preferably 600 MPa or more and 900 MPa or less. On the other hand, regarding the thermal shock resistance, when it is assumed that the four-point bending strength σ _f conforms to JIS R1601 after applying a thermal shock by quenching by dropping into water of 800 ° C. or more to 25 ° C. by the underwater dropping method according to JIS R1615 The value of σ _f / σ _i , which is the ratio between the four-point bending strength σ _f and the above-described four-point bending strength σ _i , is 0.85 or more, preferably 0.90 or more. That is, the composite ceramic of the present invention has a small decrease in strength after applying a thermal shock. Such a composite ceramic exhibiting high strength and high thermal shock resistance is particularly suitably used as a material for a member used for casting aluminum or magnesium, for example.

The ratio of σ _f and σ _i is the above-mentioned value. Regarding the value of σ _f itself, the composite ceramic of the present invention is preferably 400 MPa or more and 900 MPa or less, more preferably 500 MPa or more and 800 MPa or less. Shows a high value.

Furthermore, the composite ceramic of the present invention has high strength even at high temperatures. Specifically, the composite ceramic of the present invention has a four-point bending strength σ _h based on JIS R1604-1995, preferably at 400 ° C. or higher at high temperature, for example, 1200 ° C., more preferably 500 MPa or higher, 900 MPa or lower, More preferably, it shows a very high value of 600 MPa or more and 900 MPa or less. Thus, the composite ceramic of the present invention exhibits high strength at both room temperature and high temperature. The ratio σ _h / σ _i of the four-point bending strength sigma _i at room temperature and four-point flexural strength sigma _h at high temperatures, is preferably 0.85 or more, more preferably 0.9 or more, to 1 A close value.

The value of the four-point bending strength σ _h based on JIS R1604-1995 is measured by the following method. A test piece of JIS R1601 is prepared, and the temperature of the test piece is increased to 1200 ° C. in the atmosphere at a temperature increase rate of 200 ° C./h. After holding at 1200 ° C. for 10 minutes, a load is applied to the load point of the test piece by four-point bending at a crosshead speed of 0.5 mm / min. Measure the maximum breaking load until the specimen breaks, and let that value be σ _h .

  In addition to having the above-described characteristics, the composite ceramic of the present invention also has high oxidation resistance. The oxidation resistance can be expressed as a measure of the rate of weight increase after the composite ceramic of the present invention is oxidized. Specifically, by subtracting the weight before the oxidation treatment from the weight of the composite ceramic after the oxidation treatment at 1300 ° C. or 1400 ° C. for 100 hours in the atmosphere, dividing the result by the weight before the oxidation treatment, and multiplying by 100 The ratio of weight increase due to oxidation treatment (hereinafter, this ratio is referred to as “weight-based weight increase rate”) is calculated. A smaller increase rate means higher oxidation resistance. In the composite ceramic of the present invention, this increasing rate is preferably a small value of 0.01 to 0.10%, more preferably 0.01 to 0.08%. The range of the weight-based weight increase rate is preferably satisfied when the oxidation treatment temperature is 1300 ° C., and more preferably satisfied when the oxidation treatment temperature is 1400 ° C. in addition to the oxidation treatment temperature 1300 ° C.

The rate of weight increase due to the oxidation treatment may depend on the surface area of the composite ceramic to be measured. This is because the greater the surface area, the higher the probability of oxidation. Therefore, the ratio of weight increase calculated by subtracting the weight before oxidation treatment from the weight of the composite ceramic after oxidation treatment at 1300 ° C or 1400 ° C for 100 hours in the atmosphere and dividing it by the surface area before oxidation treatment (Hereinafter, this ratio is referred to as “surface area-based weight increase rate”) can also be used as a measure of oxidation resistance. A smaller increase rate means higher oxidation resistance. In the composite ceramic of the present invention, the increase rate of preferably 0.01~0.29g / cm ^2, more preferably a small value of 0.01~0.15g / cm ^2. The range of the surface area-based weight increase rate is preferably satisfied when the oxidation treatment temperature is 1300 ° C., and is more preferably satisfied when the oxidation treatment temperature is 1400 ° C. in addition to the oxidation treatment temperature 1300 ° C.

  The weight-based weight increase rate and the surface area-based weight increase rate are measured by the following methods. This measurement method conforms to JIS R1609-1990. First, a test piece of JIS R1601 is prepared, and the weight and surface area at 25 ° C. are measured. Next, a test piece is installed in the center soaking | uniform-heating part in a heating furnace, and the inside of a furnace is heated up to 1300 degreeC or 1400 degreeC by 200 degreeC / h. After holding at 1300 ° C. or 1400 ° C. for 100 hours, it is allowed to cool. When the specimen has cooled to room temperature, the weight is measured again. Then, based on the weight of the test piece before and after heating and the value of the surface area of the test piece before heating, the weight-based weight increase rate and the surface area-based weight increase rate are calculated according to the calculation described above.

In order to achieve the values of the above-mentioned four-point bending strengths σ _i , σ _f and σ _h , σ _f / σ _i , and weight-based weight increase rate and surface area-based weight increase rate, composite ceramics are used. The ratio of boron nitride to the whole needs to be within the above-mentioned range, and the silicate or oxynitride phase containing Y, Yb or Lu element is confirmed by X-ray diffraction, and the diffraction peak is the main. A relative integral strength of 0.01 to 0.6 with respect to the crystal phase is preferable from the viewpoint of further improving the thermal shock resistance of the composite ceramic. The present inventors consider that the inclusion of such a crystal phase in the composite ceramic increases the thermal conductivity of the composite ceramic and improves the thermal shock resistance of the composite ceramic.

  As a grain boundary phase of ordinary silicon nitride ceramics, it is known that a low melting point oxide glass phase added as an auxiliary agent is precipitated. On the other hand, in the composite ceramic of the present invention, the high-temperature stability of the composite ceramic is ensured by precipitation of a silicate or oxynitride phase crystal phase containing a Y, Yb or Lu element which is a high melting point compound, It can be a composite ceramic having excellent heat conduction. Y, Yb and Lu may be at least one of them, and it is particularly preferable to use an element having a small ionic radius among these from the viewpoint of further improving the high-temperature stability of the composite ceramic. Moreover, the thermal conductivity of the composite ceramic is further improved by the precipitation of the oxynitride phase out of the silicate phase and the oxynitride phase. In order to precipitate the silicate or oxynitride phase crystal phase containing Y, Yb or Lu elements, for example, yttrium oxide, ytterbium oxide, lutetium oxide, silicon oxide or the like can be used as a raw material when producing a composite ceramic. Good.

Examples of the silicate phase containing Y, Yb, or Lu element include Y ₂ Si ₂ O ₇ , Yb ₂ Si ₂ O _7, and Lu ₂ Si ₂ O ₇ . On the other hand, examples of the oxynitride phase containing Y, Yb, or Lu element include Y ₂ Si ₃ O ₃ N ₄ , Yb ₄ Si ₂ O ₇ N _2, and Lu ₄ Si ₂ O ₇ N ₂ . One or more kinds of crystal phases composed of these phases can be present in the composite ceramic. Whether a silicate phase or an oxynitride phase occurs in the composite ceramic depends on the ratio of each raw material used when manufacturing the composite ceramic, the firing temperature, the nitrogen partial pressure at the time of firing, and the like.

The crystal phase of the silicate phase or oxynitride phase containing the above elements has a diffraction peak relative to the main crystal phase, that is, the silicon nitride matrix, relative integrated intensity of 0.01 to 0.6, particularly 0.3. It is preferable that it exists so that it may be -0.5. Thereby, the heat conduction of the composite ceramic can be further improved. In order to realize this state, for example, a method of manufacturing a composite ceramic by adding raw materials such as yttrium oxide, ytterbium oxide, or lutetium oxide in an element ratio of a target crystal phase may be employed. The relative integrated intensity can be obtained by calculating the following equation using an X-ray diffraction pattern. In this equation, the integrated intensity of the X-ray diffraction pattern is for the main peak. The main peak of silicon nitride is about 36 degrees. The main peak of the oxynitride phase of Yb is about 29 degrees.
Relative integrated strength = integrated strength of silicate phase or oxynitride phase / integrated strength of silicon nitride matrix

  The silicate phase or oxynitride crystal phase containing the above elements is preferably present in the grain boundary phase of the silicon nitride-based ceramic matrix from the viewpoint of increasing the thermal conductivity of the composite ceramic and thus improving the thermal shock resistance. . In addition, the presence of this crystalline phase at the grain boundary of the silicon nitride-based ceramic matrix makes the oxidation protective coating formed on the surface of the composite ceramic dense and prevents oxidation from proceeding inside the ceramic. Thus, a composite ceramic with high oxidation resistance can be obtained. The presence of this crystal phase at the grain boundary of the parent phase can be confirmed by observation with a scanning electron microscope (SEM). In order to allow this crystal phase to exist in the grain boundary phase of the parent phase, for example, a method may be employed in which each raw material is mixed and molded so as to be uniformly dispersed and fired in a nitrogen atmosphere at 1700 ° C. or higher. .

As the sintering aid, the above-described silicate phase and oxynitride phase are preferably used, and combinations of Y ₂ O ₃ and Al ₂ O ₃ , combinations of Y ₂ O ₃ , MgO and TiO ₂ are used. You can also. These auxiliaries contribute to improving the strength of the composite ceramic by liquid phase sintering. However, it is preferable that the composite ceramic does not contain an Al element. Examples of the source material containing Al element include the above-described Al ₂ O ₃ and AlN. Such a substance has a function of greatly reducing the thermal conductivity by being dissolved in silicon nitride and scattering phonons, which is the main heat conduction mechanism of composite ceramics. This contributes to lowering the thermal shock resistance of the composite ceramic. For these reasons, it is preferable that the composite ceramic does not contain an Al element. The presence or absence of Al element in the composite ceramics can be confirmed by elemental analysis such as fluorescent X-ray analysis or ion emission spectroscopic analysis. In order to prevent the element from being included, it is preferable to use a material that does not contain Al as a constituent element as a raw material used in the method of manufacturing a composite ceramic described later. Ideally, the composite ceramic of the present invention does not contain any Al element. However, if the content is a very small amount of 500 ppm or less in terms of Al atom, the Al element is inevitably mixed. .

  The composite ceramic of the present invention may have fine pores. There is a distribution in pore size (pore diameter), and pores having a diameter of 1 to 10 μm are 1.5 vol. % Or less, especially 1.1 vol. % Or less, especially 0.7 vol. It is preferable that the pores exist so as to be not more than% (hereinafter, this value is referred to as “pore content”). This can increase the strength of the composite ceramic. In general, ceramics having a large number of pores having a large pore diameter tend to decrease in strength. In order to make the pore content not more than the above value, for example, a boron nitride raw material powder used in the production of composite ceramics may be of an appropriate size. The distribution of the pore diameter and the pore content are measured by image analysis or the like from a microstructural photograph obtained by SEM observation of the mirror-polished surface of the composite ceramic.

  As a result of the study by the present inventors, the shape of the pores has an influence on the performance of the composite ceramic. Further, as a result of the examination by the present inventors, the shape of the pores varies depending on the kind of the raw material powder of boron nitride which is a dispersed phase. Specifically, when t-BN is used as the raw material powder of boron nitride, substantially circular pores are generated with small isotropic properties, whereas when h-BN is used as the raw material powder of boron nitride, the anisotropy is large. An elongated pore is formed. The composite ceramics having substantially circular pores improve the strength and thermal shock resistance of the composite ceramics compared to the composite ceramics having elongated pores.

  As described above, the composite ceramic of the present invention has good thermal conductivity, and its thermal conductivity is preferably 50 W / mK or more, particularly preferably 60 W / mK or more. The larger the value of the thermal conductivity, the better. However, if the value is as large as about 70 W / mK, sufficiently satisfactory performance can be obtained. This thermal conductivity is a value measured by a laser flash method in accordance with JIS R1611. In order to achieve such a thermal conductivity value, a dispersed phase of boron nitride, which is a material with good thermal conductivity, is present, or a silicate phase or an oxynitride phase containing Y, Yb or Lu element. A crystal phase may be present in the grain boundary phase.

  Next, the suitable manufacturing method of the composite ceramic of this invention is demonstrated. This manufacturing method includes a step of mixing, forming, and firing a silicon nitride-based ceramic raw material powder forming a parent phase and a boron nitride raw material powder forming a dispersed phase. As the silicon nitride-based ceramic raw material powder, it is preferable to use a powder having an average particle size of about 0.2 to 1 μm measured using a laser diffraction particle size distribution analyzer. The same applies to the boron nitride raw material powder. The same applies to sintering aids such as yttrium oxide, ytterbium oxide, and lutetium oxide.

  The ratio of the silicon nitride-based ceramic raw material powder and the boron nitride raw material powder in the raw material is preferably set to 92: 8 to 99: 1, particularly 96: 4 to 98: 2, expressed as a weight ratio.

  These raw material powders are mixed to obtain a mixed powder, and the mixed powder is formed into a predetermined shape, for example, a plate shape or a rod shape. There is no restriction | limiting in particular in a mixing system, For example, the wet mixing using media, such as alcohol and water, is employable. For example, a ball mill or the like can be employed as the mixing device. As the molding apparatus, for example, a uniaxial press molding machine, an isotropic pressure press (CIP) apparatus, a casting molding apparatus, or the like can be adopted.

  The molded body formed into a predetermined shape is subjected to a firing step. Firing is generally performed in a nitrogen atmosphere. In this case, the nitrogen pressure is preferably about 4 to 10 atm. The firing temperature is preferably about 1700 to 2000 ° C, particularly about 1750 to 1950 ° C. The firing time at the maximum temperature is preferably about 2 to 30 hours, particularly about 6 to 12 hours.

One feature of this production method is that the boron nitride raw material powder has a small crystallite size, specifically 40 nm or more and 48 nm or less, particularly 40 nm or more and 42 nm or less. Use of such boron nitride is preferable because boron nitride is more easily dispersed in the composite ceramic. The crystallite size t mentioned here is defined by t = 0.9λ / (Bcos θ _B ). In the formula, λ represents the wavelength (nm) of the X-ray tube, B represents the full width at half maximum (rad), and θ _B represents the diffraction angle (rad).

In particular, t-BN having a turbulent layer structure that can be confirmed by an X-ray diffraction method is preferably used as the above-described boron nitride raw material powder. Since such t-BN has little shape anisotropy, boron nitride is easily dispersed uniformly in the composite ceramic. Such t-BN is also advantageous in that it promotes sintering. On the other hand, hexagonal boron nitride (h-BN) that has been conventionally used generally has a plate-like shape and therefore tends to hinder sintering. As a result, it is not easy to increase the strength of the composite ceramic. Note that the turbostratic structure in boron nitride is generally observed in the vicinity of 2θ _B = 42 ° in X-ray diffraction. In addition, t-BN which has the above-mentioned crystallite size is marketed, and is a commercially available material.

  The composite ceramics produced by the above method, utilizing the characteristics of high strength and excellent thermal shock resistance at room temperature, for example, cast members such as aluminum and magnesium, rotor members for stirring molten metal, protective tubes for heaters, etc. It is suitably used for applications.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “parts” means “parts by weight”.

[Example 1]
The raw material powder shown in Table 1 was mixed, and 150 wt% ethanol was blended with the mixed powder to form a slurry. The average particle size of each raw material powder was in the range of 0.1 to 3 μm. The obtained slurry was filled in a ball mill and mixed. After the mixing was completed, ethanol was removed by an evaporator and the mixed powder was dried. After forming the mixed powder by applying a pressure of 2 MPa using a uniaxial molding machine, a plate of 45 × 45 × 7 tmm was produced by CIP molding of 200 MPa. This plate was put in a baking furnace, heated to a maximum of 1850 ° C. in a 9 atmosphere nitrogen atmosphere (100% nitrogen gas), and held for 8 hours for baking. In this way, the intended silicon nitride based composite ceramic was obtained.

[Example 2]
The amount of Yb ₂ O ₃ raw material powder used in Example 1 was increased to 25 parts, and the amount of Si ₃ N ₄ raw material powder was reduced to 70 parts. Except for this, a composite ceramic was obtained in the same manner as in Example 1.

Example 3
The amount of Yb ₂ O ₃ raw material powder used in Example 1 was increased to 15 parts, and the amount of Si ₃ N ₄ raw material powder was reduced to 80 parts. Except for this, a composite ceramic was obtained in the same manner as in Example 1.

Example 4
The amount of the t-BN raw material powder used in Example 1 was increased to 5 parts. Except for this, a composite ceramic was obtained in the same manner as in Example 1.

Example 5
The amount of the t-BN raw material powder used in Example 1 was increased to 10 parts. Except for this, a composite ceramic was obtained in the same manner as in Example 1.

Example 6
As the t-BN raw material powder used in Example 3, a crystallite size of 47.3 nm was used. Except for this, a composite ceramic was obtained in the same manner as in Example 3.

Example 7
Instead of the t-BN raw material powder used in Example 1, h-BN raw material powder (crystallite size 48.7 nm) was used. Except for this, a composite ceramic was obtained in the same manner as in Example 1.

Example 8
Instead of the t-BN raw material powder used in Example 2, h-BN raw material powder (crystallite size 48.7 nm) was used. Except for this, a composite ceramic was obtained in the same manner as in Example 2.

Example 9
A composite ceramic was obtained in the same manner as in Example 1 except that the raw material powder shown in Table 1 was used.

Example 10
The amount of the Si ₃ N ₄ raw material powder used in Example 9 was reduced to 85 parts, and the amount of the t-BN raw material powder was increased to 7 parts. Except for this, a composite ceramic was obtained in the same manner as in Example 9.

[Comparative Example 1]
The amount of the t-BN raw material powder used in Example 3 was reduced to 1 part. Except for this, a composite ceramic was obtained in the same manner as in Example 3.

[Comparative Example 2]
The amount of the t-BN raw material powder used in Comparative Example 1 was increased to 10 parts, and the amount of the Yb ₂ O ₃ raw material powder used was reduced to 10 parts. Except for this, a composite ceramic was obtained in the same manner as in Comparative Example 1.

[Comparative Example 3]
A composite ceramic was obtained in the same manner as in Example 1 except that the raw material powder shown in Table 1 was used.

[Comparative Example 4]
Instead of the t-BN raw material powder used in Example 9, h-BN raw material powder (crystallite size 48.7 nm) was used. Except for this, a composite ceramic was obtained in the same manner as in Example 9.

[Comparative Example 5]
The amount of h-BN raw material powder used in Comparative Example 4 was increased to 5 parts. Except for this, a composite ceramic was obtained in the same manner as in Comparative Example 4.

[Evaluation]
About the composite ceramics obtained in Examples and Comparative Examples, the ratio of boron nitride, the four-point bending strength σ _i at 25 ° C., the four-point bending strength σ _h at 1200 ° C., and the four-point bending after applying thermal shock The strength σ _f , the weight-based weight increase rate, and the surface area-based weight increase rate were measured by the methods described above. In addition, the presence or absence of a crystal phase due to Al, the presence or absence of a silicate or oxylide phase, the relative integrated intensity of X-ray diffraction, and the location of the crystal phase were determined by the methods described above. Furthermore, the pore content and thermal conductivity were measured by the methods described above. These results are shown in Table 2 below.

As is clear from the results shown in Table 2, it can be seen that the composite ceramics obtained in each example have higher strength and thermal shock resistance at room temperature and higher temperature than the composite ceramics obtained in the comparative examples. . Moreover, it turns out that oxidation resistance is also high. In particular, as is clear from the comparison between Examples 1 and 2 and Examples 7 and 8, when t-BN is used as the boron nitride raw material powder, σ _i , σ _f, and _f are higher than when h-BN is used. it can be seen that the value of σ _h is high.

Claims (9)

Silicon nitride-based ceramics is used as a parent phase, and boron nitride is 2.5 vol. % Or more, 10 vol. % As a dispersed phase at a ratio of
The four-point bending strength at 25 ° C. according to JIS R1601 is σ _i , and the four-point bending strength after applying a thermal shock by quenching by dropping into water at temperatures from 800 ° C. to 25 ° C. according to JIS R1615 when was the sigma _f, the value of sigma _i is more than 400 MPa, and composite ceramics value of the ratio of σ _f / σ _i is equal to or at least 0.85.   The composite ceramic according to claim 1, wherein the composite ceramic does not contain an Al element.   2. A silicate or oxynitride phase crystal phase containing Y, Yb or Lu element is confirmed by X-ray diffraction, and its diffraction peak has a relative integrated intensity of 0.01 to 0.6 with respect to the main crystal phase. Or the composite ceramics of 2.   The composite ceramic according to any one of claims 1 to 3, wherein a crystal phase of a silicate or oxynitride phase containing Y, Yb or Lu element exists as a grain boundary phase of a silicon nitride-based ceramic matrix.   A pore having a pore diameter of 1 to 10 μm was added to 1.5 vol. The composite ceramic according to any one of claims 1 to 4, which is contained in an amount of not more than%.   The composite ceramic according to any one of claims 1 to 5, wherein the thermal conductivity measured by a laser flash method is 50 W / mK or more. When the four-point bending strength at 1200 ° C. conforming to JIS R1601 and sigma _h, the ratio σ _h / σ _i of the sigma _h and said sigma _i is not less than 0.85,
A value obtained by subtracting the weight before the oxidation treatment from the weight of the composite ceramic after the oxidation treatment at 1300 ° C. or 1400 ° C. for 100 hours in the air, dividing the result by the weight before the oxidation treatment, and multiplying by 100 is 0.01 to The composite ceramic according to any one of claims 1 to 6, wherein the content is 0.10%. It is a manufacturing method of the composite ceramics according to claim 1,
Including mixing and forming a silicon nitride-based ceramic raw material powder that forms a parent phase and a boron nitride raw material powder that forms a dispersed phase, and firing.
As boron nitride raw material powder, t = 0.9λ / (Bcos θ _B ) (where, λ represents the wavelength (nm) of the X-ray tube, B represents the half width (rad), and θ _B represents the diffraction angle ( rad).) A method for producing a composite ceramic material, wherein the crystallite size defined in (1) is 40 nm or more and less than 48 nm.   The production method according to claim 8, wherein t-BN having a turbulent structure that can be confirmed by an X-ray diffraction method is used as the boron nitride raw material powder.