【発明の詳細な説明】[Detailed description of the invention]
本発明は、高温強度の維持に優れた炭化珪素材
の接合方法に関するものである。
炭化珪素は自動車用ガスタービンエンジンの燃
焼筒やスクロール、タービンロータ部材の材料と
して目下開発が進められている材料であり、150
℃の高温に至るまで強度が低下しないという長所
を有している。かかる材料を構造材料あるいは一
般の高温工業材料として利用するには、精密寸法
や加工性の点で大形のものより小形のものが製造
しやすいので、小形物を接合して大形物とする方
法が望ましい。特に、炭化珪素粉末を焼結した炭
化珪素焼結体は、ヘリウムなどの非酸化性雰囲気
下で170℃に至るまで室温強度より低下すること
なく、むしろ室温強度の1.3〜1.6倍に増加する特
性を有し、とりわけ上記用途の使用に適する。
かような炭化珪素材を接合するには、従来技術
では接合の熱処理中接合剤に何らかの液相を生成
させ、液相の助けを借りて接合を完成させるとい
う方法をとつていた。
しかるに従来の接合方法は、接合剤としてSiの
ような金属、あるいはガラス相や不純物を比較的
多量に含んだ炭化珪素粉末を使用しているので、
高温でこれら接合層が軟化し、接合体の高温強度
を1000℃位で被接合材の本来の強度より相当低い
強度に低下させ、炭化珪素本来の性質を発揮させ
ることは難しかつた。
本発明は、上記問題を解決し、炭化珪素本来の
機械的特性を接合後においてもできる限り高温ま
で維持できるようにすることを狙つた、炭化珪素
材の接合方法を提供することを目的とする。
本発明の炭化珪素材の接合方法は、接合材とし
てホウ素または炭化ホウ素を使用し、非酸化性雰
囲気中で加熱して炭化珪素材と炭化珪素材とを結
合せしめることを特徴とする。
本発明における炭化珪素材としては、炭化珪素
の単純結晶体あるいは炭化珪素粉末を焼結した炭
化珪素焼結体などが適用できる。
接合剤して用いるホウ素あるいは炭化ホウ素
は、炭化珪素と同じ共有結合結晶に属し、しかも
約2300℃の融点を有するので、これらを単一で、
あるいは両者を合わせて用いれば、高温強度の低
下がほとんど認められない接合体を生ぜしめる。
ホウ素は1μｍより細かい、比表面積10〜90
m2／ｇのものが市販されており、これを用いる場
合にはトリクロルエチレンあるいはベンゼンのよ
うな溶媒に懸濁させて接合面に吹き付けて塗布す
ればよい。しかし、一様な厚さと密着性を保持し
た方が一層よいので、ホウ素の場合も炭化ホウ素
の場合も化学蒸着法で片方の炭化珪素の接合面と
予じめこれら接合剤をつけておけばなおよい。
炭化珪素材を接合する際には、ヘリウム、アル
ゴンなどの非酸化性ガスの雰囲気下で、炭化珪素
材と炭化珪素材との間に接合剤として用いるホウ
素または炭化ホウ素をサンドイツチ状に挾み、か
つ、炭化珪素材と接合剤とを５〜500Kg／cm2の圧
縮力で接触させて行う。結合の際の温度は、炭化
珪素と接合剤間の拡散を考慮して、1650〜2200℃
好ましくは1700〜2100℃の範囲で行われる。そし
て、結合の時間は温度により左右され一定しない
が、通常は２〜40時間で十分である。接合時の雰
囲気圧力は、通常、大気圧でよい。
以下、実施例を挙げて本発明を説明する。
実施例 １
15mm×15mm×30mmの大きさの炭化珪素焼結体
（高密度3.05ｇ／cm3で、15mm×15mmの面を蒸着面
とする）２個の各蒸着面を＃325のダイヤモンド
砥石で研削後、片方の焼結体の蒸着面に、混合気
（CH4＋BCl3＋H2）による化学蒸着法で炭化ホウ
素約30μｍの厚さに蒸着した。炭化ホウ素蒸着層
表面を1μｍダイヤモンドペーストで最終的に鏡
面研摩し、この鏡面研摩面と他方の炭化珪素焼結
体の鏡面研摩面とを５Kg／cm2で加圧して密着接触
させた後、ヘリウム雰囲気の黒鉛抵抗炉にて1700
〜2100℃間の温度に加熱した。得られた接合体か
ら接合部を中央にして３mm×４mm×30mmの試片を
切り出し、真空中で常温に従つて３点曲げ強度を
測定した。
結果をまとめて第１表に示す。
The present invention relates to a method for joining silicon carbide materials that is excellent in maintaining high-temperature strength. Silicon carbide is a material currently being developed as a material for combustion tubes, scrolls, and turbine rotor components for automobile gas turbine engines.
It has the advantage that its strength does not decrease even at high temperatures of °C. In order to use such materials as structural materials or general high-temperature industrial materials, it is easier to manufacture small pieces than large ones in terms of precision dimensions and workability, so small pieces are joined together to make large ones. method is preferred. In particular, the silicon carbide sintered body obtained by sintering silicon carbide powder has the property that its strength does not decrease below room temperature even up to 170°C in a non-oxidizing atmosphere such as helium, but rather increases to 1.3 to 1.6 times the room temperature strength. and is particularly suitable for use in the above applications. In order to bond such silicon carbide materials, the conventional technique has been to generate some kind of liquid phase in the bonding agent during heat treatment for bonding, and to complete the bond with the help of the liquid phase. However, conventional bonding methods use metals such as Si or silicon carbide powder containing relatively large amounts of glass phases and impurities as bonding agents.
These bonding layers soften at high temperatures, reducing the high-temperature strength of the bonded body to a level considerably lower than the original strength of the materials to be bonded at around 1000°C, making it difficult to bring out the original properties of silicon carbide. The present invention aims to solve the above problems and provide a method for joining silicon carbide materials, which aims to maintain the inherent mechanical properties of silicon carbide up to as high a temperature as possible even after joining. . The method for bonding silicon carbide materials of the present invention is characterized in that boron or boron carbide is used as a bonding material, and the silicon carbide materials are bonded together by heating in a non-oxidizing atmosphere. As the silicon carbide material in the present invention, a simple crystal of silicon carbide or a sintered silicon carbide body obtained by sintering silicon carbide powder can be used. Boron or boron carbide used as a bonding agent belongs to the same covalent bond crystal as silicon carbide and has a melting point of about 2300°C, so they can be used alone.
Alternatively, if both are used in combination, a bonded body with almost no decrease in high-temperature strength is produced. Boron is finer than 1μm, specific surface area 10-90
m 2 /g is commercially available, and when used, it can be applied by suspending it in a solvent such as trichloroethylene or benzene and spraying it onto the joint surface. However, it is better to maintain uniform thickness and adhesion, so in the case of both boron and boron carbide, it is best to apply these bonding agents to the bonding surface of one silicon carbide in advance using the chemical vapor deposition method. Even better. When bonding silicon carbide materials, boron or boron carbide used as a bonding agent is sandwiched between the silicon carbide materials in a sandwich shape in an atmosphere of non-oxidizing gas such as helium or argon. In addition, the silicon carbide material and the bonding agent are brought into contact with each other under a compressive force of 5 to 500 kg/cm 2 . The temperature during bonding is 1650-2200℃ considering the diffusion between silicon carbide and bonding agent.
Preferably it is carried out at a temperature in the range of 1700 to 2100°C. Although the bonding time varies depending on the temperature, 2 to 40 hours is usually sufficient. The atmospheric pressure during bonding may normally be atmospheric pressure. The present invention will be explained below with reference to Examples. Example 1 Each vapor deposition surface of two silicon carbide sintered bodies (high density 3.05 g/cm 3 , 15 mm x 15 mm surface is the vapor deposition surface) with a size of 15 mm x 15 mm x 30 mm was placed on a #325 diamond whetstone. After grinding, boron carbide was deposited to a thickness of about 30 μm on the deposition surface of one of the sintered bodies by chemical vapor deposition using a mixture (CH 4 +BCl 3 +H 2 ). The surface of the boron carbide deposited layer is finally mirror-polished with 1 μm diamond paste, and this mirror-polished surface and the mirror-polished surface of the other silicon carbide sintered body are brought into close contact by pressurizing at 5 kg/cm 2 , and then helium is applied. 1700 in graphite resistance furnace with atmosphere
Heated to a temperature between ~2100°C. A specimen measuring 3 mm x 4 mm x 30 mm was cut out from the resulting joined body with the joint at the center, and its three-point bending strength was measured in vacuum at room temperature. The results are summarized in Table 1.
【表】
表から本発明実施例の接合体は、曲げ強度が室
温に比べて1500℃で若干の強度低下が認められた
が、従来品では３〜４割の低下がまぬがれなかつ
たことからすれば著しく改善されている。
なお、上記混合気となつた混合気（BCl3＋H2）
でホウ素を蒸着して同様な方法によつて接合させ
た場合も、ほぼ同様な結果を得た。
実施例 ２
実施例１と同じように鏡面研摩した炭化珪素焼
結体の研摩面に、85m2／ｇの比表面積の非晶質ホ
ウ素粉末をベンゼンを分散媒として霧状に吹き付
け、厚さ約30μｍのホウ素層を作つた。ホウ素層
を別の鏡面研摩炭化珪素焼結体で挾み、両焼結体
を500Kg／cm2の加圧下で実施例１と同様に加熱し
た。接合体の強度は表より１〜２割低かつたが、
室温に対しての高温強度の低下は同表程度で小さ
かつた。
実施例 ３
実施例１の炭化ホウ素層または実施例２のホウ
素の厚さを5μｍ以下に形成して接合すると、中
間層が残留しない炭化珪素同士の直接結合体にほ
ぼ近いものが得られた。この接合体の曲げ強度
は、実施例１の結果より１〜２割程度向上した。
実施例 ４
炭化珪素の単結晶体も上記実施例と同様に接合
できた。この接合体の曲げ強度も、上記表と同傾
向であつたが、高温で強度が同表よりも２〜３割
大きくなつた。
破壊状況を観察すると上記全ての実施例で得ら
れた接合体の曲げテストでは、接合界面から割れ
る例は稀で、界面近傍の炭化珪素側で割れてい
た。これは界面の強度が実用に耐え得ることを意
味している。
以上述べたような本発明方法は、炭化珪素と同
じ共有結合結晶に属し、しかも約2300℃の融点を
有するホウ素あるいは炭化ホウ素を接合剤として
用いるので、接合後において2300℃の高温まで接
合剤に液相の生成がなく、炭化珪素材の機械的特
性を維持し、かつ、高温強度の低下たとえば非酸
化性雰囲気下で1500℃程度の高温まで強度低下が
ほとんど認められない炭化珪素材の接合体を得る
ことができ、炭化珪素材の接合方法として好適で
ある。[Table] As shown in the table, the bending strength of the joined body of the example of the present invention was slightly decreased at 1500℃ compared to room temperature, whereas the conventional product could not avoid a decrease of 30 to 40%. It has been significantly improved. In addition, the mixture that became the above mixture (BCl 3 + H 2 )
Almost the same results were obtained when boron was vapor-deposited and bonded using the same method. Example 2 Amorphous boron powder with a specific surface area of 85 m 2 /g was sprayed in the form of a mist using benzene as a dispersion medium onto the polished surface of a silicon carbide sintered body that had been mirror-polished in the same manner as in Example 1, to a thickness of approximately A 30μm boron layer was created. The boron layer was sandwiched between another mirror-polished silicon carbide sintered body, and both sintered bodies were heated in the same manner as in Example 1 under a pressure of 500 Kg/cm 2 . Although the strength of the bonded body was 10 to 20% lower than the table,
The decrease in high-temperature strength relative to room temperature was as small as in the same table. Example 3 When the boron carbide layer of Example 1 or the boron of Example 2 was formed to a thickness of 5 μm or less and bonded, a product almost like a direct bond of silicon carbide without any residual intermediate layer was obtained. The bending strength of this joined body was improved by about 10 to 20% compared to the result of Example 1. Example 4 Single crystals of silicon carbide could also be joined in the same manner as in the above example. The bending strength of this joined body also showed the same tendency as in the table above, but at high temperatures the strength was 20 to 30% greater than that in the table. Observing the fracture status, in the bending tests of the bonded bodies obtained in all of the above examples, cracks rarely occurred from the bond interface, and cracks occurred on the silicon carbide side near the interface. This means that the strength of the interface is sufficient for practical use. The method of the present invention as described above uses boron or boron carbide as a bonding agent, which belongs to the same covalent bond crystal as silicon carbide and has a melting point of about 2300℃, so the bonding agent can be used up to a high temperature of 2300℃ after bonding. A joined body of silicon carbide material that does not generate a liquid phase, maintains the mechanical properties of the silicon carbide material, and shows almost no decrease in high-temperature strength, for example, up to a high temperature of about 1500°C in a non-oxidizing atmosphere. This method is suitable as a method for joining silicon carbide materials.