WO2010113555A1 - Silicon nitride-based composite ceramic and process for producing same - Google Patents

Silicon nitride-based composite ceramic and process for producing same Download PDF

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Publication number
WO2010113555A1
WO2010113555A1 PCT/JP2010/052417 JP2010052417W WO2010113555A1 WO 2010113555 A1 WO2010113555 A1 WO 2010113555A1 JP 2010052417 W JP2010052417 W JP 2010052417W WO 2010113555 A1 WO2010113555 A1 WO 2010113555A1
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composite ceramic
phase
raw material
boron nitride
composite
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PCT/JP2010/052417
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French (fr)
Japanese (ja)
Inventor
井筒　靖久
英紀 北
秀樹 日向
近藤　直樹
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三井金属鉱業株式会社
独立行政法人産業技術総合研究所
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Priority to CN201080001148.7A priority Critical patent/CN101959831B/en
Publication of WO2010113555A1 publication Critical patent/WO2010113555A1/en

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Definitions

  • 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.
  • a composite with boron nitride has been attempted.
  • 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.
  • normal hexagonal boron nitride h-BN
  • h-BN normal hexagonal boron nitride
  • a mixture of silicon nitride powder and boron nitride powder is added and mixed with ⁇ sialon powder, aluminum nitride powder and rare earth element oxide powder as sintering aids, respectively.
  • a method for producing a composite ceramic to be sintered has been proposed (see Patent Document 1).
  • silicon nitride powder and boron nitride powder are mixed in a weight ratio of 90:10 to 70:30.
  • urea and boric acid are used at the time of production, and hydrogen treatment is required, so the process becomes complicated. Moreover, not only are facilities limited, but they can be dangerous. Further, the document 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.
  • an object of the present invention is to provide a silicon nitride-based composite ceramic that can eliminate the various drawbacks of the above-described prior art.
  • 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
  • the four-point bending strength at 25 ° C. according to JIS R1601 is ⁇ i
  • 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 forming a parent phase and a boron nitride raw material powder forming a dispersed phase, followed by firing.
  • 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.
  • 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 ⁇ -silicon nitride.
  • boron nitride is compounded as a dispersed phase.
  • Boron nitride which is 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.
  • 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.
  • the composite ceramic of the present invention has high strength and excellent thermal shock resistance.
  • the strength of a ceramic material is evaluated by a four-point bending strength in accordance with JIS R1601, and the composite ceramic of the present invention has a four-point bending strength ⁇ i of 400 MPa or more at room temperature, for example, 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.
  • the thermal shock resistance when it is assumed that the four-point bending strength ⁇ f conforms to JIS R1601 after applying a thermal shock by quenching by dropping into water of 800 ° C.
  • the composite ceramic of the present invention has a small decrease in strength after applying a thermal shock.
  • 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 ⁇ f and ⁇ i is the above-mentioned value.
  • 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.
  • the composite ceramic of the present invention has high strength even at high temperatures.
  • the composite ceramic of the present invention has a four-point bending strength ⁇ h in accordance with 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.
  • the composite ceramic of the present invention exhibits high strength at both room temperature and high temperature.
  • the ratio ⁇ h / ⁇ i between the four-point bending strength ⁇ h at a high temperature and the four-point bending strength ⁇ i at room temperature is preferably 0.85 or more, more preferably 0.9 or more, A close value.
  • the value of the four-point bending strength ⁇ h according to 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.
  • 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 ⁇ h .
  • 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.
  • this increase 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.
  • this increasing rate is preferably a small value of 0.01 to 0.29 g / cm 2 , more preferably 0.01 to 0.15 g / 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.
  • a test piece of JIS R1601 is prepared, and the weight and surface area at 25 ° C. are measured.
  • a test piece is installed in the center soaking
  • 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.
  • the composite ceramic of the present invention 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 precipitates.
  • 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.
  • 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.
  • a 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 is 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 .
  • 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 with a relative integrated intensity of 0.01 to 0.6, particularly 0.3, relative to the main crystal phase, that is, the silicon nitride matrix. Preferably it is present to be .about.0.5. Thereby, the heat conduction of the composite ceramic can be further improved.
  • 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.
  • 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. .
  • 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).
  • each raw material is mixed and molded so as to be uniformly dispersed and fired in a nitrogen atmosphere at 1700 ° C. or higher. .
  • 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.
  • the composite ceramic does not contain an Al element.
  • 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.
  • 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.
  • elemental analysis such as fluorescent X-ray analysis or ion emission spectroscopic analysis.
  • the composite ceramic of the present invention does not contain any Al element.
  • 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.
  • pore sizes pore diameter
  • pores having a diameter of 1 to 10 ⁇ m are 1.5 vol. % Or less, especially 1.1 vol. % Or less, especially 0.7 vol.
  • pore content this value is referred to as “pore content”
  • ceramics having a large number of pores having a large pore diameter tend to decrease in strength.
  • 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.
  • the shape of the pores described above affects 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. More specifically, when t-BN is used as the raw material powder of boron nitride, substantially circular pores with low isotropicity are generated, 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.
  • the composite ceramic of the present invention has a good thermal conductivity, and its thermal conductivity is preferably 50 W / mK or more, particularly preferably 60 W / mK or more.
  • This thermal conductivity is a value measured by a laser flash method in accordance with JIS R1611.
  • 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.
  • 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.
  • a 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 ⁇ m measured using a laser diffraction type particle size distribution analyzer.
  • sintering aids such as yttrium oxide, ytterbium oxide, and lutetium oxide.
  • the ratio of the silicon nitride-based ceramic raw material powder to 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 this mixed powder is formed into a predetermined shape, for example, a plate shape or a rod shape.
  • a mixing system For example, the wet mixing using media, such as alcohol and water, is employable.
  • a ball mill or the like can be employed as the mixing device.
  • 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 process. 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.
  • 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.
  • t-BN having a turbulent layer structure that can be confirmed by an X-ray diffraction method is preferably used as the above-mentioned 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.
  • h-BN hexagonal boron nitride
  • t-BN having the crystallite size described above is commercially available 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.
  • 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 ⁇ m.
  • 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 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 The t-BN raw material powder used in Example 3 had a crystallite size of 47.3 nm. 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.
  • Example 1 The amount of 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 was decreased to 10 parts. Except for this, a composite ceramic was obtained in the same manner as in Comparative Example 1.
  • 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.
  • 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.
  • a silicon nitride-based composite ceramic having high strength at both room temperature and high temperature and excellent in thermal shock resistance and oxidation resistance.

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Abstract

A composite ceramic which 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 2.5-10 vol.%. When the four-point bending strength as measured at 25ºC in accordance with JIS R1601 is expressed by σi and the four-point bending strength as measured after a thermal shock is applied thereto by quenching from 800ºC or higher through dropping into 25ºC water by the dropping-into-water method according to JIS R1615 is expressed by σf, then the value of σi is 400 MPa or higher and the ratio of σf/oi is 0.85 or higher.

Description

窒化ケイ素基複合セラミックス及びその製造方法Silicon nitride based composite ceramics and method for producing the same
　本発明は、アルミニウムやマグネシウム等の鋳造部材として好適な窒化ケイ素基複合セラミックス及びその製造方法に関する。 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.
　窒化ケイ素セラミックスは、高強度、高硬度、耐熱性、耐腐食性に優れることから、多くの工業分野で応用化されている。また、窒化ケイ素セラミックスの耐熱衝撃性を改善するために、窒化ホウ素との複合化が試みられている。しかしながら、窒化ホウ素は窒化ケイ素ガラス成分との濡れ性が悪いので、これを大量に添加すると焼結性が低下し、高い強度を有する緻密な材料を得ることが困難であった。また、通常の六方晶窒化ホウ素（ｈ－ＢＮ）は板状の結晶形態を有し、窒化ケイ素焼結体に分散した場合、窒化ホウ素の形状が鋭角となり欠陥として作用するため、材料本来の強度が低下するという問題点があった。そこで、これらの問題解決を図るための取り組みがなされてきた。 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 an acute angle and acts as a defect. There has been a problem of lowering. Therefore, efforts have been made to solve these problems.
　例えば、耐熱衝撃性を向上させる目的で、窒化ケイ素粉末と窒化ホウ素粉末との混合物に、βサイアロン粉末、窒化アルミニウム粉末及び希土類元素の酸化物粉末を各々焼結助剤として添加混合して成形した後、焼結する複合セラミックスの製造方法が提案されている（特許文献１参照）。この製造方法においては、窒化ケイ素粉末と窒化ホウ素粉末とを、重量比で９０：１０～７０：３０の割合で混合している。 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.
　この技術とは別に、窒化ケイ素マトリックスの結晶粒内及び／又は粒界に、微細な六方晶窒化ホウ素を均一に分散させた窒化ケイ素基複合材料も提案されている（特許文献２参照）。この複合材料においては、六方晶窒化ホウ素の含有割合が窒化ケイ素基複合材料の１～２５ｖｏｌ．％になっている。同文献には、この構成を採用することで、この複合材料は、破壊強度や耐熱衝撃性などの機械的強度が大幅に改善されると記載されている。 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. In this document, it is described that by adopting this configuration, the composite material is greatly improved in mechanical strength such as fracture strength and thermal shock resistance.
特開平６－１００３６９号公報Japanese Patent Application Laid-Open No. 6-1003009 特開平９－１６９５７５号公報JP-A-9-169575
　しかし、特許文献１に記載の技術においては、通常の板状結晶である六方晶窒化ホウ素を添加しているので、焼結体内部の窒化ホウ素はそのアスペクト比が大きく、それに起因して破壊源として作用してしまう。その結果、複合セラミックスの強度が低下してしまう。 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.
　特許文献２に記載の技術においては、製造時に尿素及びホウ酸を使用しており、また水素処理が必要であることから工程が煩雑となる。そのうえ、設備が制限されるばかりでなく、危険を伴うこともある。更に、同文献には、六方晶窒化ホウ素の含有割合が窒化ケイ素基複合材料の１～２５ｖｏｌ．％であると記載はされているものの、具体的な例として記載されている割合の下限値は５ｖｏｌ．％の場合までであり、５ｖｏｌ．％未満の場合については具体的な効果が確認されていない。しかも同文献には、耐熱衝撃性に関する効果についての記載はあるものの、その効果は具体的に例証されていない。 In the technique described in Patent Document 2, urea and boric acid are used at the time of production, and hydrogen treatment is required, so the process becomes complicated. Moreover, not only are facilities limited, but they can be dangerous. Further, the document 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.
　したがって発明の目的は、前述した従来技術が有する種々の欠点を解消し得る窒化ケイ素基複合セラミックスを提供することにある。 Therefore, an object of the present invention is to provide a silicon nitride-based composite ceramic that can eliminate the various drawbacks of the above-described prior art.
　本発明は、窒化ケイ素基セラミックスを母相とし、窒化ホウ素が２．５ｖｏｌ．％以上、１０ｖｏｌ．％以下の割合で分散相として複合されており、
　ＪＩＳ　Ｒ１６０１に準拠した２５℃での四点曲げ強度をσi、ＪＩＳ　Ｒ１６１５に準拠した水中投下法によって８００℃以上から２５℃の水中に投下による急冷で熱衝撃を与えた後の四点曲げ強度をσfとしたとき、σiの値が４００ＭＰａ以上で、かつσf／σiの比の値が０．８５以上であることを特徴とする複合セラミックスを提供するものである。 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
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 rapid cooling by dropping into water at temperatures from 800 ° C. to 25 ° C. according to JIS R1615 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.
　また本発明は、上記の複合セラミックスの好適な製造方法として、
　母相を形成する窒化ケイ素基セラミックス原料粉末と分散相を形成する窒化ホウ素原料粉末を混合して成形し、焼成する工程を含み、
　窒化ホウ素原料粉末として、ｔ＝０．９λ／（ＢｃｏｓθB）（式中、λはＸ線管球の波長（ｎｍ）を表し、Ｂは半値幅（ｒａｄ）を表し、θBは回折角（ｒａｄ）を表す。）で定義される結晶子サイズが４０ｎｍ以上、４８ｎｍ未満のものを用いることを特徴とする複合セラミックスの製造方法を提供するものである。 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 forming a parent phase and a boron nitride raw material powder forming a dispersed phase, followed by 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.
　以下本発明を、その好ましい実施形態に基づき説明する。本発明の複合セラミックスは、窒化ケイ素基セラミックスを母相としたものである。この母相は一般にβ－窒化ケイ素から構成されている。そして、この母相中に窒化ホウ素が分散相として複合されている。母相である窒化ケイ素中に窒化ホウ素を分散相として複合化させることで、窒化ケイ素単体の場合に比べて室温下及び高温下（例えば６００～１４００℃）での強度や、耐熱衝撃性及び耐酸化性が向上する。 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 combining boron nitride as a dispersed phase in silicon nitride, which is the parent phase, strength at room temperature and high temperature (for example, 600 to 1400 ° C.), thermal shock resistance and acid resistance compared to the case of silicon nitride alone. Improves conversion.
　分散相である窒化ホウ素は、複合セラミックス全体に対して２．５ｖｏｌ．％以上、１０ｖｏｌ．％以下の割合で、概ね均一に、かつ微細な状態で含まれている。窒化ホウ素の割合が２．５ｖｏｌ．％に満たないと、複合セラミックス中に窒化ホウ素が全体に均一に分散せず耐熱衝撃性が改善されない。逆に１０ｖｏｌ．％を超えると、窒化ケイ素の焼結性が低下し、破壊強度が低くなる。一層高強度で、かつ耐熱衝撃性に優れた複合セラミックスを得る観点から、複合セラミックス全体に対する窒化ホウ素の割合は２．５ｖｏｌ．％以上、５ｖｏｌ．％以下であることが好ましい。複合セラミックス中における窒化ホウ素の割合は、Ｘ線回折や波長分散型元素分析等によって測定することができる。 Boron nitride, which is 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.
　上述したとおり、本発明の複合セラミックスは高強度で、かつ耐熱衝撃性に優れたものである。一般にセラミックス材料の強度は、ＪＩＳ　Ｒ１６０１に準拠した四点曲げ強度によって評価されるところ、本発明の複合セラミックスは、該四点曲げ強度σiが、室温下、例えば２５℃において４００ＭＰａ以上であり、好ましくは５００ＭＰａ以上、９００ＭＰａ以下、更に好ましくは６００ＭＰａ以上、９００ＭＰａ以下という非常に高い値を示す。一方、耐熱衝撃性に関しては、ＪＩＳ　Ｒ１６１５に準拠した水中投下法によって８００℃以上から２５℃の水中に投下による急冷で熱衝撃を与えた後のＪＩＳ　Ｒ１６０１に準拠した四点曲げ強度σfとすると、該四点曲げ強度σfと先に述べた四点曲げ強度σiとの比であるσf／σiの値が０．８５以上であり、好ましくは０．９０以上となっている。つまり、本発明の複合セラミックスは、熱衝撃を与えた後の強度低下が小さいものである。このような高強度、高耐熱衝撃性を示す複合セラミックスは、例えばアルミニウムやマグネシウムの鋳造に用いられる部材の材料として特に好適に用いられる。 As described above, the composite ceramic of the present invention has high strength and excellent thermal shock resistance. Generally, the strength of a ceramic material is evaluated by a four-point bending strength in accordance with 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, 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 submerged dropping method conforming 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.
　σfとσiの比は上述の値となっているところ、σfの値そのものに関しても、本発明の複合セラミックスは、好ましくは４００ＭＰａ以上、９００ＭＰａ以下、更に好ましくは５００ＭＰａ以上、８００ＭＰａ以下という非常に高い値を示す。 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.
　更に本発明の複合セラミックスは、高温下においても高強度のものである。具体的には、本発明の複合セラミックスは、ＪＩＳ　Ｒ１６０４－１９９５に準拠した四点曲げ強度σhが、高温下、例えば１２００℃において好ましくは４００ＭＰａ以上であり、更に好ましくは５００ＭＰａ以上、９００ＭＰａ以下、一層好ましくは６００ＭＰａ以上、９００ＭＰａ以下という非常に高い値を示す。このように、本発明の複合セラミックスは、室温下及び高温下のいずれにおいても高強度を示す。高温下での四点曲げ強度σhと室温下
での四点曲げ強度σiとの比率σh／σiは、好ましくは０．８５以上、更に好ましくは０．９以上であり、１に近い値となる。 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 in accordance with 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 between the four-point bending strength σ h at a high temperature and the four-point bending strength σ i at room temperature is preferably 0.85 or more, more preferably 0.9 or more, A close value.
　ＪＩＳ　Ｒ１６０４－１９９５に準拠した四点曲げ強度σhの値は次の方法で測定される。ＪＩＳ　Ｒ１６０１の試験片を用意し、この試験片を、大気中、２００℃／ｈの昇温速度で１２００℃まで昇温する。１２００℃で１０分間保持した後、試験片の荷重点に、クロスヘッド速度０．５ｍｍ／ｍｉｎにて四点曲げで荷重を加える。試験片が破壊するまでの最大破壊荷重を測定し、その値をσhとする。 The value of the four-point bending strength σ h according to 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 .
　上述した特性を有することに加え、本発明の複合セラミックスは耐酸化性が高いものでもある。耐酸化性は、本発明の複合セラミックスを酸化処理した後の重量増の割合を尺度として表すことができる。具体的には、大気中で１３００℃又は１４００℃・１００時間酸化処理した後の複合セラミックスの重量から酸化処理前の重量を差し引き、それを酸化処理前の重量で除して１００を乗じることで、酸化処理による重量増の割合（以下、この割合を「重量基準重量増加率」という）が算出される。この増加率が小さいほど、耐酸化性が高いことを意味する。本発明の複合セラミックスにおいては、この増加率が好ましくは０．０１～０．１０％、更に好ましくは０．０１～０．０８％という小さな値となる。この重量基準重量増加率の範囲は、酸化処理温度１３００℃のときに満たされることが好ましく、酸化処理温度１３００℃に加えて、酸化処理温度１４００℃のときにも満たされることが更に好ましい。 In addition to having the characteristics described above, 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 increase 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.
　前記の酸化処理による重量増の割合は、測定対象となる複合セラミックスの表面積に依存する場合がある。表面積が大きいほど、酸化される確率が高くなるからである。そこで、大気中で１３００℃又は１４００℃・１００時間酸化処理した後の複合セラミックスの重量から酸化処理前の重量を差し引き、それを酸化処理前の表面積で除すことで算出される重量増の割合（以下、この割合を「表面積基準重量増加率」という）を、耐酸化性の尺度として用いることもできる。この増加率が小さいほど、耐酸化性が高いことを意味する。本発明の複合セラミックスにおいては、この増加率が好ましくは０．０１～０．２９ｇ／ｃｍ2、更に好ましくは０．０１～０．１５ｇ／ｃｍ2という小さな値となる。この表面積基準重量増加率の範囲は、酸化処理温度１３００℃のときに満たされることが好ましく、酸化処理温度１３００℃に加えて、酸化処理温度１４００℃のときにも満たされることが更に好ましい。 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, this increasing rate is preferably a small value of 0.01 to 0.29 g / cm 2 , more preferably 0.01 to 0.15 g / 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.
　重量基準重量増加率及び表面積基準重量増加率は次の方法で測定される。本測定方法はＪＩＳ　Ｒ１６０９－１９９０に準じる。まずＪＩＳ　Ｒ１６０１の試験片を用意し、２５℃での重量及び表面積を測定する。次に試験片を加熱炉内の中央の均熱部に設置し、炉内を２００℃／ｈで１３００℃又は１４００℃まで昇温する。１３００℃又は１４００℃で１００時間保持した後に放冷する。試験片が室温まで冷却したら重量を再び測定する。そして、加熱前後の試験片の重量及び加熱前の試験片の表面積の値に基づき、上述した計算に従い重量基準重量増加率及び表面積基準重量増加率を算出する。 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 being kept 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.
　上述した四点曲げ強度σi、σf及びσhの値や、σf／σiの値、更には重量基準重量増加率及び表面積基準重量増加率の値を達成するためには、複合セラミックス全体に対する窒化ホウ素の割合が上述した範囲内であることが必要であり、またＹ、Ｙｂ又はＬｕ元素を含むシリケート又はオキシナイトライド相の結晶相がＸ線回折によって確認され、その回折ピークが主要結晶相に対して相対積分強度０．０１～０．６であることが、複合セラミックスの耐熱衝撃性を一層高める点から好ましい。このような結晶相が複合セラミックス中に含まれていることによって、複合セラミックスの熱伝導性が高まり、複合セラミックスの耐熱衝撃性が向上するものと、本発明者らは考えている。 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.
　通常の窒化ケイ素セラミックスの粒界相としては、助剤として添加した低融点酸化物ガラス相が析出することが知られている。これに対して本発明の複合セラミックスにおいては、高融点化合物であるＹ、Ｙｂ又はＬｕ元素を含むシリケート又はオキシナイトライド相の結晶相が析出することで、複合セラミックスの高温安定性が確保され、熱伝導に優れた複合セラミックスとなすことができる。Ｙ、Ｙｂ及びＬｕは、これらのうちの少なくとも１種を用いればよく、特にこれらのうちイオン半径の小さな元素を用いることが、複合セラミックスの高温安定性の一層の向上の点から好ましい。また、シリケート相及びオキシナイトライド相のうち、オキシナイトライド相が析出することで、複合セラミックスの熱伝導が一層良好になる。Ｙ、Ｙｂ又はＬｕ元素を含むシリケート又はオキシナイトライド相の結晶相を析出させるためには、複合セラミックスを製造するときの原料として、例えば酸化イットリウム、酸化イッテルビウム及び酸化ルテチウムや酸化ケイ素などを用いればよい。 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 precipitates. 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 deposit a 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 is used as a raw material when producing a composite ceramic. Good.
　Ｙ、Ｙｂ又はＬｕ元素を含むシリケート相としては、例えばＹ2Ｓｉ2Ｏ7やＹｂ2Ｓｉ2Ｏ7及びＬｕ2Ｓｉ2Ｏ7などが挙げられる。一方、Ｙ、Ｙｂ又はＬｕ元素を含むオキシナイトライド相としては、例えばＹ2Ｓｉ3Ｏ3Ｎ4やＹｂ4Ｓｉ2Ｏ7Ｎ2及びＬｕ4Ｓｉ2Ｏ7Ｎ2などが挙げられる。これらの相からなる結晶相は、複合セラミックス中に１種又は２種以上存在することができる。複合セラミックス中にシリケート相が生ずるか、それともオキシナイトライド相が生ずるかは、複合セラミックスを製造するときに用いられる各原料の比率、焼成温度、焼成時の窒素分圧等に依存する。 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.
　上記の元素を含むシリケート相やオキシナイトライド相の結晶相は、その回折ピークが、主要結晶相、すなわち窒化ケイ素母相に対して、相対積分強度０．０１～０．６、特に０．３～０．５であるように存在していることが好ましい。これによって、複合セラミックスの熱伝導を一層良好にすることができる。この状態を実現するためには、例えば酸化イットリウム、酸化イッテルビウム又は酸化ルテチウムなどの原料を、狙いとする結晶相の元素比で加えて、複合セラミックスを製造するという手段を採用すればよい。前記の相対積分強度は、Ｘ線回折パターンを用いて次式を計算することで得られる。この式中、Ｘ線回折パターンの積分強度は、そのメインピークを対象とするものである。窒化ケイ素のメインピークは約３６度である。また、Ｙｂのオキシナイトライド相のメインピークは約２９度である。
相対積分強度＝シリケート相又はオキシナイトライド相の積分強度／窒化ケイ素母相の積分強度 The crystal phase of the silicate phase or oxynitride phase containing the above elements has a diffraction peak with a relative integrated intensity of 0.01 to 0.6, particularly 0.3, relative to the main crystal phase, that is, the silicon nitride matrix. Preferably it is present to be .about.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
　上記の元素を含むシリケート相やオキシナイトライド相の結晶相は、窒化ケイ素基セラミックス母相の粒界相に存在することが、複合セラミックスの熱伝導を高め、ひいては耐熱衝撃性を高める点から好ましい。また、この結晶相が窒化ケイ素基セラミックス母相の粒界に存在することで、複合セラミックス表層に形成される酸化防護被膜を緻密なものとし、セラミックス内部に酸化が進行することが阻止され、それによって耐酸化性の高い複合セラミックスとなすことができる。この結晶相が母相の粒界に存在することは走査型電子顕微鏡（ＳＥＭ）観察によって確認することができる。この結晶相を母相の粒界相に存在させるためには、例えば、各原料を均一に分散するように混合して成形し、１７００℃以上の窒素雰囲気で焼成するという手段を採用すればよい。 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. .
　焼結助剤としては、上述したシリケート相やオキシナイトライド相が好適に用いられる他、Ｙ2Ｏ3やＡｌ2Ｏ3の組み合わせや、Ｙ2Ｏ3、ＭｇＯ及びＴｉＯ2の組み合わせ等を用いることもできる。これらの助剤は、液相焼結して複合セラミックスの強度を向上させることに寄与する。尤も、複合セラミックスは、Ａｌ元素を含まないことが好ましい。Ａｌ元素を含む原料物質としては、例えば上述のＡｌ2Ｏ3やＡｌＮ等がある。このような物質は、窒化ケイ素中に固溶し、複合セラミックスの主たる熱伝導機構であるフォノンを散乱させることで熱伝導率を大きく低下させる作用を有しているので、該物質の存在によって、複合セラミックスの耐熱衝撃性を低下させる一因になる。このような理由によって、複合セラミックス中には、Ａｌ元素が含まれないことが好ましい。複合セラミックス中におけるＡｌ元素の存在の有無は、例えば蛍光Ｘ線分析やイオン発光分光分析等の元素分析によって確認することができる。該元素が含まれないようにするためには、後述する複合セラミックスの製造方法において用いられる原料物質として、Ａｌを構成元素としないものを用いることが好ましい。本発明の複合セラミックスは、Ａｌ元素を全く含まないことが理想的であるが、Ａｌ原子換算で５００ｐｐｍ以下のごく微量の含有量であれば、Ａｌ元素が不可避的に混入することは許容される。 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. .
　本発明の複合セラミックスは微細な気孔を有する場合がある。気孔の大きさ（気孔径）には分布があり、該径が１～１０μｍの気孔が１．５ｖｏｌ．％以下、特に１．１ｖｏｌ．％以下、とりわけ０．７ｖｏｌ．％以下となるように、該気孔が存在していることが好ましい（以下、この値を「気孔含有率」という。）これによって、複合セラミックスの強度を高めることができる。一般に、気孔径が大きな気孔を多数有しているセラミックスは、強度が低下する傾向にある。気孔含有率を、上記の値以下とするためには、例えば複合セラミックスの製造において用いられる窒化ホウ素原料粉末として、適切な大きさのものを用いればよい。気孔径の分布及び気孔含有率は、複合セラミックスの鏡面研磨面をＳＥＭ観察して得られる微構造組織写真から画像解析等によって測定される。 The composite ceramic of the present invention may have fine pores. There is a distribution of pore sizes (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 are present so as to be not more than% (hereinafter, this value is referred to as “pore content”), whereby the strength of the composite ceramic can be increased. 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.
　上記の気孔に関しては、その形状が複合セラミックスの性能に影響を及ぼすことが本発明者らの検討の結果判明した。また、気孔の形状は、分散相である窒化ホウ素の原料粉末の種類によって変化することも、本発明者らの検討の結果判明した。詳細には、窒化ホウ素の原料粉末としてｔ－ＢＮを用いると、等方性の小さい略円形の気孔が生じるのに対し、窒化ホウ素の原料粉末としてｈ－ＢＮを用いると、異方性の大きな細長い形状の気孔が生じる。そして、細長い形状の気孔を有する複合セラミックスよりも略円形の気孔を有する複合セラミックスの方が、複合セラミックスの強度や耐熱衝撃性が向上する。 As a result of the examination by the present inventors, the shape of the pores described above affects 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. More specifically, when t-BN is used as the raw material powder of boron nitride, substantially circular pores with low isotropicity are generated, 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.
　本発明の複合セラミックスが熱伝導の良好なものであることは先に述べたとおりであるところ、その熱伝導率は５０Ｗ／ｍＫ以上、特に６０Ｗ／ｍＫ以上であることが好ましい。熱伝導率の値は、大きければ大きいほど好ましいが、７０Ｗ／ｍＫ程度に大きい値であれば、十分に満足すべき性能が得られる。この熱伝導率は、ＪＩＳ　Ｒ１６１１に準拠してレーザーフラッシュ法によって測定された値である。このような熱伝導率の値を達成するためには、熱伝導の良好な材料である窒化ホウ素の分散相を存在させたり、あるいはＹ、Ｙｂ又はＬｕ元素を含むシリケート相やオキシナイトライド相の結晶相を粒界相に存在させたりすればよい。 As described above, the composite ceramic of the present invention has a 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.
　次に、本発明の複合セラミックスの好適な製造方法について説明する。本製造方法は、母相を形成する窒化ケイ素基セラミックス原料粉末と分散相を形成する窒化ホウ素原料粉末を混合して成形し、焼成する工程を含むものである。窒化ケイ素基セラミックス原料粉末としては、レーザー回折式粒度分布測定装置を用いて測定された平均粒径が０．２～１μｍ程度のものを用いることが好ましい。窒化ホウ素原料粉末についても同様である。また、酸化イットリウム、酸化イッテルビウム、酸化ルテチウム等の焼結助剤についても同様である。 Next, a preferred method for producing the composite ceramic of the present invention will be described. 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 type 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.
　原料中における窒化ケイ素基セラミックス原料粉末と窒化ホウ素原料粉末との比率は、重量比で表して、９２：８～９９：１、特に９６：４～９８：２に設定することが好ましい。 The ratio of the silicon nitride-based ceramic raw material powder to 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.
　これらの原料粉末を混合して混合粉体を得、この混合粉体を所定の形状、例えば板状や棒状などに成形する。混合方式に特に制限はなく、例えばアルコールや水などの媒体を用いた湿式混合を採用することができる。混合装置には、例えばボールミル等を採用することができる。成形装置には、例えば一軸プレス成形機、等方圧加圧プレス（ＣＩＰ）装置及びキャスティング成形装置等を採用することができる。 These raw material powders are mixed to obtain a mixed powder, and this 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.
　所定の形状に成形された成形体は焼成工程に付される。焼成は一般に窒素雰囲気下で行われる。この場合、窒素の圧力は４～１０気圧程度とすることが好ましい。焼成温度は１７００～２０００℃程度、特に１７５０～１９５０℃程度とすることが好ましい。最高温度での焼成時間は２～３０時間程度、特に６～１２時間程度とすることが好ましい。 The molded body formed into a predetermined shape is subjected to a firing process. 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.
　本製造方法は、窒化ホウ素原料粉末として、結晶子サイズが微小のもの、具体的には４０ｎｍ以上、４８ｎｍ以下、特に４０ｎｍ以上、４２ｎｍ以下のものを用いることを特徴の１つとしている。かかる窒化ホウ素を用いると、複合セラミックス中において窒化ホウ素が一層均一に分散しやすくなるので好ましい。ここで言う結晶子サイズｔとは、ｔ＝０．９λ／（ＢｃｏｓθB）で定義される。式中、λはＸ線管球の波長（ｎｍ）を表し、Ｂは半値幅（ｒａｄ）を表し、θBは回折角（ｒａｄ）を表す。 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).
　特に上述の窒化ホウ素原料粉末として、Ｘ線回折法によって確認できる乱層構造を有するｔ－ＢＮを用いることが好ましい。かかるｔ－ＢＮは形状異方性が少ないので、複合セラミックス中において窒化ホウ素が均一に分散しやすくなる。また、かかるｔ－ＢＮは焼結を促進させる点でも有利である。これに対して、従来用いられていた六方晶窒化ホウ素（ｈ－ＢＮ）は、一般に板状の形状をしているので焼結を妨げる傾向がある。その結果、複合セラミックスの強度を高めることは容易ではない。なお、窒化ホウ素における乱層構造は、Ｘ線回折において一般に２θB＝４２°付近に観察される。なお、上述の結晶子サイズを有するｔ－ＢＮは市販されており、商業的に入手可能な材料である。 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-mentioned 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. Note that t-BN having the crystallite size described above is commercially available and is a commercially available material.
　以上の方法によって製造された複合セラミックスは、室温下における高強度及び優れた耐熱衝撃性という特徴を活かして、例えばアルミニウムやマグネシウム等の鋳造部材、金属溶湯撹拌用のローター部材、ヒーター用保護管等の用途に好適に用いられる。 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.
　以下、実施例により本発明を更に詳細に説明する。しかしながら、本発明の範囲は、かかる実施例に制限されない。特に断らない限り、「部」は「重量部」を意味する。 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”.
　　〔実施例１〕
　表１に示す原料粉末を混合し、混合粉末に対して１５０重量％のエタノールを配合してスラリーとなした。各原料粉末の平均粒径は０．１～３μｍの範囲であった。得られたスラリーをボールミルに充填して混合した。混合完了後、エバポレーターによってエタノールを除去して混合粉末を乾燥した。一軸成形機を用い混合粉末に２ＭＰａの圧力を加えて成形した後、２００ＭＰａのＣＩＰ成形によって４５×４５×７ｔｍｍのプレートを作製した。このプレートを焼成炉に入れて、９気圧の窒素雰囲気（１００％窒素ガス）中、最高１８５０℃まで昇温し、８時間保持して焼成した。このようにして、目的とする窒化ケイ素基複合セラミックスを得た。 [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.
　　〔実施例２〕
　実施例１において用いたＹｂ2Ｏ3原料粉末の使用量を２５部に増量し、かつＳｉ3Ｎ4原料粉末の使用量を７０部に減量した。これ以外は実施例１と同様にして複合セラミックスを得た。 [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.
　　〔実施例３〕
　実施例１において用いたＹｂ2Ｏ3原料粉末の使用量を１５部に増量し、かつＳｉ3Ｎ4原料粉末の使用量を８０部に減量した。これ以外は実施例１と同様にして複合セラミックスを得た。 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.
　　〔実施例４〕
　実施例１において用いたｔ－ＢＮ原料粉末の使用量を５部に増量した。これ以外は実施例１と同様にして複合セラミックスを得た。 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.
　　〔実施例５〕
　実施例１において用いたｔ－ＢＮ原料粉末の使用量を１０部に増量した。これ以外は実施例１と同様にして複合セラミックスを得た。 Example 5
The amount of 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.
　　〔実施例６〕
　実施例３において用いたｔ－ＢＮ原料粉末として、結晶子サイズが４７．３ｎｍのものを用いた。これ以外は実施例３と同様にして複合セラミックスを得た。 Example 6
The t-BN raw material powder used in Example 3 had a crystallite size of 47.3 nm. Except for this, a composite ceramic was obtained in the same manner as in Example 3.
　　〔実施例７〕
　実施例１において用いたｔ－ＢＮ原料粉末に代えて、ｈ－ＢＮ原料粉末（結晶子サイズ４８．７ｎｍ）を用いた。これ以外は実施例１と同様にして複合セラミックスを得た。 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.
　　〔実施例８〕
　実施例２において用いたｔ－ＢＮ原料粉末に代えて、ｈ－ＢＮ原料粉末（結晶子サイズ４８．７ｎｍ）を用いた。これ以外は実施例２と同様にして複合セラミックスを得た。 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.
　　〔実施例９〕
　表１に示す原料粉末を用いた以外は実施例１と同様にして複合セラミックスを得た。 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.
　　〔実施例１０〕
　実施例９において用いたＳｉ3Ｎ4原料粉末の使用量を８５部に減量し、かつｔ－ＢＮ原料粉末の使用量を７部に増量した。これ以外は実施例９と同様にして複合セラミックスを得た。 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.
　　〔比較例１〕
　実施例３において用いたｔ－ＢＮ原料粉末の使用量を１部に減量した。これ以外は実施例３と同様にして複合セラミックスを得た。 [Comparative Example 1]
The amount of 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.
　　〔比較例２〕
　比較例１において用いたｔ－ＢＮ原料粉末の使用量を１０部に増量し、かつＹｂ2Ｏ3原料粉末の使用量を１０部に減量した。これ以外は比較例１と同様にして複合セラミックスを得た。 [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 was decreased to 10 parts. Except for this, a composite ceramic was obtained in the same manner as in Comparative Example 1.
　　〔比較例３〕
　表１に示す原料粉末を用いた以外は実施例１と同様にして複合セラミックスを得た。 [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.
　　〔比較例４〕
　実施例９において用いたｔ－ＢＮ原料粉末に代えて、ｈ－ＢＮ原料粉末（結晶子サイズ４８．７ｎｍ）を用いた。これ以外は実施例９と同様にして複合セラミックスを得た。 [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.
　　〔比較例５〕
　比較例４において用いたｈ－ＢＮ原料粉末の使用量を５部に増量した。これ以外は比較例４と同様にして複合セラミックスを得た。 [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.
　　〔評価〕
　実施例及び比較例で得られた複合セラミックスについて、窒化ホウ素の割合、２５℃での四点曲げ強度σi、１２００℃での四点曲げ強度σh、熱衝撃を与えた後の四点曲げ強度σf、重量基準重量増加率及び表面積基準重量増加率を、上述の方法で測定した。また、Ａｌに起因する結晶相の有無、シリケート又はオキシライド相の有無、Ｘ線回折の相対積分強度及び該結晶相の存在位置を、上述の方法で求めた。更に、気孔含有率及び熱伝導率を、上述の方法で測定した。これらの結果を以下の表２に示す。 [Evaluation]
About the composite ceramics obtained in Examples and Comparative Examples, the ratio of boron nitride, four-point bending strength σ i at 25 ° C., four-point bending strength σ h at 1200 ° C., four-point bending after applying thermal shock strength sigma f, the weight percent weight increase and surface area basis weight increase rate was measured by the method 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.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　表２に示す結果から明らかなように、各実施例で得られた複合セラミックスは、比較例で得られた複合セラミックスに比べて室温下及び高温下での強度並びに耐熱衝撃性が高いことが判る。また、耐酸化性も高いことが判る。特に、実施例１及び２と実施例７及び８との対比から明らかなように、窒化ホウ素原料粉末として、ｔ－ＢＮを用いると、ｈ－ＢＮを用いた場合よりもσi、σf及びσhの値が高くなることが判る。 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 apparent from comparison of Examples 1 and 2 and Examples 7 and 8, as the boron nitride material powder, the use of t-BN, also sigma i than with h-BN, sigma f and It can be seen that the value of σ h increases.
　本発明によれば、室温及び高温のいずれにおいても高強度で、かつ耐熱衝撃性及び耐酸化性に優れた窒化ケイ素基複合セラミックスが提供される。 According to the present invention, there is provided a silicon nitride-based composite ceramic having high strength at both room temperature and high temperature and excellent in thermal shock resistance and oxidation resistance.

Claims (9)

  1. 　窒化ケイ素基セラミックスを母相とし、窒化ホウ素が２．５ｖｏｌ．％以上、１０ｖｏｌ．％以下の割合で分散相として複合されており、
    　ＪＩＳ　Ｒ１６０１に準拠した２５℃での四点曲げ強度をσi、ＪＩＳ　Ｒ１６１５に準拠した水中投下法によって８００℃以上から２５℃の水中に投下による急冷で熱衝撃を与えた後の四点曲げ強度をσfとしたとき、σiの値が４００ＭＰａ以上で、かつσf／σiの比の値が０．８５以上であることを特徴とする複合セラミックス。     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 rapid cooling 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.
  2. 　上記複合セラミックス中にＡｌ元素が含まれていない請求項１記載の複合セラミックス。 The composite ceramic according to claim 1, wherein the composite ceramic contains no Al element.
  3. 　Ｙ、Ｙｂ又はＬｕ元素を含むシリケート又はオキシナイトライド相の結晶相がＸ線回折によって確認され、その回折ピークが主要結晶相に対して相対積分強度０．０１～０．６である請求項１記載の複合セラミックス。 The crystal phase of a silicate or oxynitride phase containing a Y, Yb or Lu element is confirmed by X-ray diffraction, and the diffraction peak thereof has a relative integrated intensity of 0.01 to 0.6 with respect to the main crystal phase. The composite ceramic described.
  4. 　Ｙ、Ｙｂ又はＬｕ元素を含むシリケート又はオキシナイトライド相の結晶相が窒化ケイ素基セラミックス母相の粒界相として存在する請求項１記載の複合セラミックス。 The composite ceramic according to claim 1, wherein a crystal phase of a silicate or oxynitride phase containing a Y, Yb or Lu element exists as a grain boundary phase of a silicon nitride-based ceramic matrix.
  5. 　気孔径１～１０μｍの気孔を１．５ｖｏｌ．％以下で含む請求項１記載の複合セラミックス。 気 1.5 vol. Of pores with a pore diameter of 1-10 μm. The composite ceramic according to claim 1, which is contained in an amount of not more than%.
  6. 　レーザーフラッシュ法によって測定した熱伝導率が５０Ｗ／ｍＫ以上である請求項１記載の複合セラミックス。 The composite ceramic according to claim 1, wherein the thermal conductivity measured by a laser flash method is 50 W / mK or more.
  7. 　ＪＩＳ　Ｒ１６０１に準拠した１２００℃での四点曲げ強度をσhとしたとき、σhと前記のσiとの比率σh／σiが０．８５以上であり、
    　大気中で１３００℃又は１４００℃・１００時間酸化処理した後の複合セラミックスの重量から酸化処理前の重量を差し引き、それを酸化処理前の重量で除して１００を乗じた値が０．０１～０．１０％である請求項１記載の複合セラミックス。     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 atmosphere, dividing the result by the weight before the oxidation treatment, and multiplying by 100 is 0.01 to The composite ceramic according to claim 1, wherein the content is 0.10%.
  8. 　請求項１に記載の複合セラミックスの製造方法であって、
    　母相を形成する窒化ケイ素基セラミックス原料粉末と分散相を形成する窒化ホウ素原料粉末を混合して成形し、焼成する工程を含み、
    　窒化ホウ素原料粉末として、ｔ＝０．９λ／（ＢｃｏｓθB）（式中、λはＸ線管球の波長（ｎｍ）を表し、Ｂは半値幅（ｒａｄ）を表し、θBは回折角（ｒａｄ）を表す。）で定義される結晶子サイズが４０ｎｍ以上、４８ｎｍ未満のものを用いることを特徴とする複合セラミックスの製造方法。     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 forming a parent phase and a boron nitride raw material powder forming a dispersed phase, followed by 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.
  9. 　窒化ホウ素原料粉末として、Ｘ線回折法によって確認できる乱層構造を有するｔ－ＢＮを用いる請求項８記載の製造方法。 The production method according to claim 8, wherein t-BN having a turbulent layer structure that can be confirmed by an X-ray diffraction method is used as the boron nitride raw material powder.
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