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

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

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JP2010254545A
JP2010254545A JP2009248179A JP2009248179A JP2010254545A JP 2010254545 A JP2010254545 A JP 2010254545A JP 2009248179 A JP2009248179 A JP 2009248179A JP 2009248179 A JP2009248179 A JP 2009248179A JP 2010254545 A JP2010254545 A JP 2010254545A
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composite ceramic
phase
raw material
boron nitride
composite
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JP4667520B2 (en
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Yasuhisa Izutsu
靖久 井筒
Hidenori Kita
英紀 北
Hideki Hiuga
秀樹 日向
Naoki Kondo
直樹 近藤
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Mitsui Mining and Smelting Co Ltd
National Institute of Advanced Industrial Science and Technology AIST
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Mitsui Mining and Smelting Co Ltd
National Institute of Advanced Industrial Science and Technology AIST
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Priority to KR1020107018754A priority patent/KR101540751B1/en
Priority to CN201080001148.7A priority patent/CN101959831B/en
Priority to PCT/JP2010/052417 priority patent/WO2010113555A1/en
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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

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 acute 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. 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.

特開平6−100369号公報JP-A-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 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.

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。   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.

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
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.

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 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.

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。   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.

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 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.

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 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.

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. 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.

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 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.

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 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 .

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 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.

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, 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.

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 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.

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 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.

Y、Yb又はLu元素を含むシリケート相としては、例えばY2Si27やYb2Si27及びLu2Si27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Y2Si334やYb4Si272及びLu4Si272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 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

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、Y23やAl23の組み合わせや、Y23、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Al23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 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.

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 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.

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 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, 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.

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 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.

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 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.

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 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.

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-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.

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Yb23原料粉末の使用量を25部に増量し、かつSi34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Yb23原料粉末の使用量を15部に増量し、かつSi34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 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.

〔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
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.

〔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Si34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 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.

〔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Yb23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 used was reduced 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, 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.

Figure 2010254545
Figure 2010254545

Figure 2010254545
Figure 2010254545

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 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)

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 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.
上記複合セラミックス中にAl元素を含まない請求項1に記載の複合セラミックス。   The composite ceramic according to claim 1, wherein the composite ceramic does not contain an Al element. 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又は2に記載の複合セラミックス。   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. 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ないし3のいずれかに記載の複合セラミックス。   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. 気孔径1〜10μmの気孔を1.5vol.%以下で含む請求項1ないし4のいずれかに記載の複合セラミックス。   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%. 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ないし5のいずれかに記載の複合セラミックス。   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. 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ないし6のいずれかに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 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%.
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 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.
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に記載の製造方法。   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.
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