JP2004090130A - JOINING METHOD FOR TiAL-BASE ALLOY AND STEEL PRODUCT - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost and simple joining method, which directly joins a TiAl-base alloy and a steel product for realizing the improvement in transient response characteristic of a light and small supercharger, elevation of a turbine inlet temperature and high speed rotation, and is excellent in high temperature strength suitable for use at a high temperature. <P>SOLUTION: This joining method for the TiAl-base alloy and the steel product, includes the steps of: heating a turbine wheel 1 provided with a recessed joining part 3 and made of a TiAl-base alloy member, cooling a shaft 2 provided with a projecting joining part 4 and made of a steel product member, or performing both of the above to give a temperature difference to both members; and pushing the projecting joining part 4 in the recessed joining part 3 and the returning the temperature to an ordinary temperature. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【産業上の利用分野】
本発明は、ＴｉＡｌ基合金と鋼材の接合方法に関する。特には、本発明は乗用車、トラック用小型過給機のタービンホイールおよび船舶用大型過給機、ジェットエンジン、産業用ガスタービンブレード等のタービンの製造におけるＴｉＡｌ基合金と鋼材の接合方法に関する。
【０００２】
【従来技術】
近年の環境問題への関心の高まりから、乗用車、トラック、船舶などの輸送機械に用いられる過給機の性能向上が、またジェットエンジン、産業用ガスタービンなどの効率の向上が求められている。上記製品の性能、効率を支配する重要な構成要素の一つはタービンであり、近年このタービンに対し、過渡応答特性の向上、タービン入り口温度の高温化および高速回転化などが求められている。
【０００３】
これらの性能向上に有望な材料として、従来から用いられているＮｉ基超合金よりも軽量で、慣性モーメントが小さく、高温強度が高い、金属間化合物ＴｉＡｌを主相とする合金（本明細書中では、ＴｉＡｌ基合金という）がある。そのため、ＴｉＡｌ基合金をタービンホイールとし、粘り強さがあり、加工が容易な素材である鋼材をシャフトとして、これらを接合してなるガスタービン等が好ましく用いられる。
【０００４】
しかし、このようなタービンを製造するには、ＴｉＡｌ基合金のタービンホイールと、鋼材シャフトとを接合する必要がある。ＴｉＡｌ基合金と鋼材とは溶接等によって直接には接合できないため、このタービンホイールを鋼材からなるシャフトに接合するための技術が重要となる。
【０００５】
特開平２−１５７４０３号公報は、ＴｉＡｌ基合金からなるタービンホイールと鋼材からなるシャフトとの間に中間材を設け、ＴｉＡｌ基合金と中間材の接合は摩擦接合で、中間材とシャフトとの接合は電子ビーム溶接で行う接合方法を提案している。かかる方法では中間材として、ＴｉＡｌ基合金と接合性の良好なインコロイ９０９（商品名）等を用いている。しかし、この方法では接合対象となる部材に加えて中間材を必要とし、ＴｉＡｌ基合金と中間材とのそれぞれに機械加工をする必要があるため、接合コストが高いことが問題であった。
【０００６】
特開２０００−２０２６８３号公報は、ロウ付けを接合手段として用いるＴｉＡｌ基合金と鋼材の接合方法を開示している。かかる方法では、軸方向に垂直な面のみならず、周方向にも接合面を形成し、周方向の接合面には低強度のロウ材を用いて、ロウ材自体の塑性変形で凝固時に発生する応力を緩和するものである。このとき、軸方向に垂直な接合面においてはこの応力は負荷されないため、高温に長時間曝される接合部の仕様に鑑み、耐久性維持のため高強度のロウ材を用いた接合構造を提供している。しかし、この方法においても、ロウ自体にも材料費がかかり、ロウ付けを真空下で実施する必要があるため、接合コストが高いことが問題であった。
【０００７】
【発明が解決しようとする課題】
小型過給機等の過渡応答特性の向上、タービン入り口温度の高温化および高速回転化を実現し得るＴｉＡｌ基合金と、鋼材とを接合する低コストで簡便な方法を提供することを目的とする。また、高温での使用に適した、高温強度に優れた接合方法を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明は、上記課題を解決するためになされたものであって、凹状接合部が設けられたＴｉＡｌ基合金部材を加熱することにより、あるいは、凸状接合部が設けられた鋼材部材を冷却することにより、あるいはこれらの両方を行うことにより、該ＴｉＡｌ基合金部材と該鋼材部材とに温度差を与えるステップと、該凸状接合部を、該凹状接合部に押し込むステップとを含むＴｉＡｌ基合金と鋼材の接合方法をも提供する。前記温度差が、４００〜１２００℃であることが好ましい。押し込み後、加熱あるいは冷却した部材を常温に戻すことにより、接合された状態となる。
【０００９】
ここでいう接合とは、凸状接合部と凹状接合部を構成する材料間の成分の混合が生じる、いわゆる冶金的な接合ではなく、熱収縮を利用して凸状接合部と凹状接合部との界面が密着して固定される機械的な接合である。
【００１０】
前記凸状接合部に突起部を設け、該突起部に嵌合するように前記凹状結合部に溝部を設けることがさらに好ましい。
【００１１】
また、凹状接合部が設けられた鋼材部材と凸状接合部が設けられたＴｉＡｌ基合金部材とを相対的に回転させることにより、該凸状接合部を、該凹状接合部に押し込むステップを含むＴｉＡｌ基合金と鋼材の接合方法である。前記回転が、２０００〜３０００ｒｐｍであることが好ましい。押し込み後、回転の摩擦によって昇温された部材を常温に戻すことにより、接合された状態となる。
【００１２】
前記凸状接合部に突起部を設けることがさらに好ましい。
【００１３】
また、本発明に係るＴｉＡｌ基合金と鋼材の接合方法においては、ＴｉＡｌ基合金部材がタービンのタービンホイールであり、前記鋼材部材がタービンのシャフトであることが好ましい。ここで、タービンには、乗用車、トラック、船舶などの輸送機械に用いられる過給機、ジェットエンジン、産業用ガスタービンを含む。
【００１４】
本発明によれば、材料間の成分の混合が生じると非常に脆い相が生成するために、直接接合出来ない材料どうしであるＴｉＡｌ基合金と鋼材とを、別途に中間材を必要とすることなく、両材料の線膨張率の差を利用することで接合することができる。かかる方法では、運転時に接合部が置かれる環境に合わせて、接合部の形状や、接合条件を調整することで、運転時に接合が緩むことなく、強度の高い接合を可能にする。また、接合の対象となる二つの部材に加えて、従来技術のようにさらなる部材を必要とすることなく、接合部の煩雑な加工も必要でない簡便にかつ低コストで実現できる接合方法を提供する。
【００１５】
【発明の実施の形態】
以下に、実施形態を挙げて本発明を詳細に説明する。同じ部材には同じ符号を付して示す。
【００１６】
本発明の第一の実施形態にかかるＴｉＡｌ基合金と鋼材の接合方法は、凹状接合部が設けられたＴｉＡｌ基合金部材を加熱するか、凸状接合部が設けられた鋼材部材を冷却するか、あるいはこの両方を行うかして、両部材に温度差を与えるステップと、該凸状接合部を、前記凹状接合部に押し込むステップとを含む。
【００１７】
図１に、第一の実施形態の方法により接合されたタービンホイールとシャフトの断面を示す。ＴｉＡｌ基合金からなるタービンホイール１は接合される側の端部に凹状接合部３を有する。鋼材からなるシャフト２は、接合される側の端部に凸状接合部４を有する。
【００１８】
ここで、ＴｉＡｌ基合金とは、Ｔｉを主な構成元素とし、Ａｌを２８〜３５重量％含み、その他にＮｂ、Ｃｒ、Ｍｎ、Ｓｉ、Ｗ、Ｃ、Ｂなどの添加元素を含んでもよい合金である。鋼材とは、鉄を主な構成元素とし、その他にＣ、Ｃｒ、Ｍｎ、Ｓｉ、Ｎｉ、Ｓ、Ｂなどの添加元素を含んでもよい合金である。
【００１９】
凹状接合部３と凸状接合部４は、押し込み後、常温に戻った時点で強固に接合されるようなサイズに予め加工される。すなわち、凸状接合部４が凹状接合部３より若干大きくなるように加工される。ただし、本実施形態では、塑性変形させながら凸状接合部４を押し込むものではないため、金槌等で軽く叩くだけで凸状接合部４を凹状接合部３に挿入できる必要がある。つまり、押し込み時には、凸状接合部４よりも凹状接合部３の方が大きい必要がある。
【００２０】
この、押し込み時と常温に戻った後において、両接合部の大きさの関係を逆転させるためには、押し込み時において、凹状接合部３が設けられたＴｉＡｌ基合金部材が、凸状接合部４が設けられた鋼材部材より、高温となるような所定の温度差を与える必要がある。
【００２１】
ここで、ある温度における線膨張率はＴｉＡｌ基合金と鋼材とで異なる。図４にＴｉＡｌ基合金と鋼材との線膨張係数の関係を示す。実際に凸状接合部４と凹状接合部３との加工を行う場合には、部材のサイズと図４のグラフから計算して、凸状接合部４と凹状接合部３のサイズならびに、温度を決定することが好ましい。例えば、まず常温で行う部材加工時においては、径で０．０５ｍｍ凸状接合部４の方が、凹状接合部３より大きくなるように加工する。
【００２２】
次に、ＴｉＡｌ基合金部材を加熱することで凹状接合部３を膨張により大きくし、あるいは鋼材部材を冷却することで収縮により凸状接合部４を小さくし、凹状接合部３の膨張量と凸状接合部４の収縮量を足した値が０．１ｍｍとなれば、押し込み時には凹状接合部の方が０．０５ｍｍ大きくなるため、金槌等で叩けば容易に押し込むことができる。
【００２３】
また、押し込み後、常温に戻った時点では部材のサイズは元に戻るので、凸状接合部４の方が、凹状接合部３より０．０５ｍｍ大きくなり、界面が密着することとなる。すなわち、強固に接合することができる。
【００２４】
第一の実施形態においては、押し込み時の両部材の温度差は４００〜１２００℃であることが望ましい。４００℃以下では凹状接合部３が、凸状接合部４よりも十分大きくないため、金槌で叩いた程度では押し込むことはできない。また、１２００℃以上とするためには、鋼材部材を冷却するにしても、ＴｉＡｌ基合金を１０５０℃以上に加熱しなければならない。この場合、耐熱性が高いＴｉＡｌ基合金といえども、酸化量が大きくなるとともに、焼鈍効果によって材料強度が低下するため望ましくない。押し込み後は、そのまま放置することにより、常温に戻し、強固に接合した状態とすることができる。
【００２５】
以上述べた内容は、これまで一般的に行われている通常の焼きばめと一見同じであるが、以下に述べる効果がＴｉＡｌ基合金と鋼材部材の組合せのみによって得られるものであり、これを見出した点が本発明の主眼である。
【００２６】
かかる第一の実施形態に係る方法において、凸状接合部４には、突出した突起部を設け、凹状接合部３には、突出した突起部に嵌合する溝部を設けて、第一の実施形態で説明したのと同様の方法で、両部材に温度差を設けることにより、接合を実施することができる。この突起部ならびに溝部がある状態では、加熱後に上から叩くだけではこれらが抵抗となって押し込むことはできない。そこで、雄ねじ雌ねじの関係となるように、突起部と溝部を加工しておき、回転させながら押し込む必要がある。
【００２７】
かかる突起部と溝部とを設けることにより、接合後においては、密着した界面の面積が大きくなるとともに、引っ張った際には突起部と溝部によって抵抗力が増大するため、凸状接合部４と凹状接合部３とが外れにくくなる。すなわち、接合強度が向上する。さらには、一般にタービン等の回転部品は一方向のみに回転することから、突起部と溝部のねじの関係を、回転に対して逆ねじにしておけば、その効果によって使用時の接合部の信頼性をさらに向上させることができる。
【００２８】
小型過給機等に用いられるＴｉＡｌ基合金部材は一般に高温で使用されるため、シャフトとの接合部も高温化する。第一の実施形態においては、接合後において、内部に線膨張率が大きい鋼材部材が、また外部には線膨張率が小さいＴｉＡｌ基部材が配置されているため、高温での使用に特に適している。すなわち、接合部が高温化した場合、内部の鋼材部材の膨張量の方が、外部のＴｉＡｌ基部材よりも大きくなるため、接合界面がさらに押しつけられることとなり、密着性が向上し接合強度は向上する。すなわち、温度上昇とともに接合強度が向上するという、通常では生じ得ないことが、本実施形態でのＴｉＡｌ基合金部材と鋼材部材の接合部では生じるため、かかる実施形態による接合を行うことが有利である。
【００２９】
次に、本発明の第二の実施形態について説明する。第二の実施形態にかかるＴｉＡｌ基合金と鋼材の接合方法は、凹状接合部が設けられた鋼材部材と凸状接合部が設けられたＴｉＡｌ基合金部材とを相対的に回転させることにより、該凸状接合部を、該凹状接合部に押し込むステップを含む。
【００３０】
図２に第二の実施形態の方法により接合されたタービンホイールとシャフトとの接合界面の形状を示す断面図である。タービンホイール１はＴｉＡｌ基合金からなり、接合される側の端部に凸状接合部５を有する。シャフト２は鋼材からなり、接合される側の端部に凹状接合部６を有する。
【００３１】
タービンホイール１の凸状接合部５とシャフト２の凹状接合部６とは、凸接合部５の先端部が凹状接合部６の穴よりも若干大きくなるように予め加工される。本実施形態では凸状接合部５を回転させながら押し込むことによって摩擦熱が生じ、凸状接合部５と凹状接合部６との両方が加熱された状態で押し込むことができる。また、接合後、常温に戻る際の熱収縮によって、凸状接合部５と凹状接合部６の界面が密着することによって、接合部が強固に固定される。
【００３２】
ここで、図４に示すグラフより、鋼材の線膨張率の方がＴｉＡｌ基合金の線膨張率より大きいため、押し込み後の冷却過程においては、外側の鋼材の収縮量の方が内側のＴｉＡｌ基合金の収縮量より大きくなり、外側から締め付けられることになるため、界面が密着して強固に接合される。
【００３３】
この第二の実施形態においては、凸状接合部５は凹部接合部６よりも大きい必要があるが、サイズの精度は重要ではない。つまり、凸状接合部５を形成する、硬く、高温強度が高いＴｉＡｌ基合金を、凹部接合部６を形成する、柔らかく、高温強度が低い鋼材に、相対的に回転させながら力ずくに押し込むため、鋼材の塑性変形が生じるため、凹部接合部が多少狭くても、押し広げることが可能となるためである。
【００３４】
以上に述べたように、この発明の第二の実施形態は、通常の金属材料同士では実現不可能な接合方法であり、ＴｉＡｌ基合金と鋼材という、全く異なる高温強度と線膨張率を持つ材料の組合せのみにおいて実現できる接合方法であり、これを見出した点が本発明の主眼である。
【００３５】
つまり、通常の金属材料同士では、類似の高温強度を有しているため、回転させながら押し込んでも、凹部接合部６のみが塑性変形して凸部接合部５がその形状を維持しながら入り込むというような効果は得られない。また、押し込み後、常温に冷却した時点でも、外側と内側の部材の収縮量は同じであるため、締め付け力は発生しないため、界面は密着せず、強固な接合力は得られない。
【００３６】
シャフト２とタービンホイール１とを相対的に回転させることにより、該凸状接合部５を、該凹状接合部６に押し込むステップは、シャフト２を固定し、タービンホイール１を、回転を与える装置に装着して、凸状接合部５を回転させながら、凹状接合部６にねじ込むようにすることができる。しかし、本発明にかかる方法では、相対的に回転するようにして押し込めば良いので、シャフト２を回転させ、タービンホイール１を固定しても同じ効果が得られる。
【００３７】
回転数は２０００〜３０００ｒｐｍとすることが好ましい。２０００ｒｐｍ以下では摩擦による加熱が不十分であり、冷却後において、十分な締め付け力が発生するに必要な程の温度上昇をもたらすことができない。また、３０００ｒｐｍ以上では温度が上昇しすぎ、特に耐熱性が低い鋼材部材が、著しく酸化するとともに、焼鈍作用によって材料強度が低下することから望ましくない。前述の条件でタービンホイール１を回転させながら凸状接合部５を凹状接合部６に押し込むのに要する時間は、通常、２０〜３０秒である。
【００３８】
この第二の実施形態に係る方法によれば、通常の摩擦接合装置が利用できるため、簡便でコストもかからない。さらには、凸状接合部５と凹状接合部６との加工精度の厳密さが要求されないため、シャフト２とタービンホイール１の加工の段階でも有利である。
【００３９】
第三の実施形態にかかるＴｉＡｌ基合金と鋼材の接合方法は、第二の実施形態に係る方法において、凸状接合部に突起部を設けることを特徴とする。
【００４０】
図３に第三の実施形態に示した回転して押し込む方法によりタービンホイール１とシャフト２が接合された状態の断面図を示す。接合前の部材加工の段階において、タービンホイール１に設けられた凸状接合部７には、突出した突起部９が設けられる。この突起部９の形状は角のある形状でもよく、曲面を有する形状でもよい。また、微小な突起部９が複数設けられてもよい。なお、鋼材部材の凹状接合部８については、この時点では特に溝を加工する必要はなく、第二の実施形態と同様の形状でよい。
【００４１】
これら部材の接合は、第二の実施形態で説明したのと同様に実施される。押し込み時には、硬く高温強度が高いＴｉＡｌ基合金の凸状接合部７の突起部９は変形せずに初期の形状が維持されるが、柔らかく高温強度の低い鋼材部材の凹状接合部８は塑性変形が生じる。この塑性変形は凸状接合部７の突起部９に対応する形状となるため、最終的には溝部の形状となる。かかる突起部９を設けることにより、接合後においては密着した界面の面積が大きくなるとともに、引っ張った際には突起部９と、突起部によりできた溝部によって抵抗力が増大するため、凸状接合部７と凹状接合部８とが外れにくくなる。すなわち、接合強度が向上する。
【００４２】
【実施例】
以下に、本発明の実施例について説明する。かかる実施例は本発明を限定するものではない。
【００４３】
［実施例１］
本実施例は第一の実施形態に関するものである。直径２５ｍｍのＴｉＡｌ基合金の棒材と、直径２５ｍｍの鋼材の棒材を用いて試験した。ＴｉＡｌ基合金の成分は、Ｔｉ−３１．３重量％Ａｌ−７．０重量％Ｎｂ−１．３重量％Ｃｒであり、精密鋳造後、鋳造欠陥消滅のため１２５０℃でＨＩＰ処理を行ったものである。一方、鋼材部材は、成分がＦｅ−０．４５重量％Ｃ−１．５重量％Ｍｎ−０．３重量％Ｓの硫黄快削鋼（規格：ＡＩＳＩ−Ｃ１１４４）である。
【００４４】
凸状接合部４を有する部材は主に鋼材を用い、先端が直径１０ｍｍで高さ５ｍｍの円筒となるような凸形状に加工した。また外周の径は２０ｍｍにそろえた。一方、凹状接合部３を有する部材については、主にＴｉＡｌ基合金を用い、先端が直径９．９５ｍｍで高さ５ｍｍの円筒穴となるような凹形状に加工した。また外周の径は同様に２０ｍｍにそろえた。さらに、比較のために、形状は上記と同じままで、ＴｉＡｌ基合金どうし、および鋼材どうしについても試験した。
【００４５】
これらの試験片を電気炉に入れて加熱、あるいは液体窒素に入れて冷却した後に、凸状接合部を有する部材を、凹状接合部を有する部材の上に置いた状態で、金槌で軽く叩き、可能なものについては押し込んだ。押し込み量は凸部先端が凹部底面についた状態が最大で５ｍｍとなった。
【００４６】
接合条件は表１に示した条件である。評価内容は、まず金槌で軽く叩いて押し込めるかどうかとした。押し込めたものについては、そのまま放置して冷却し、常温付近になってから接合装置から取り外した。このようにして得た接合部材の評価としては、外観状況の目視観察ならびに継手引張試験を実施した。継手引引張試験では接合部から離れた両部材の外周部にねじを切り、このねじをつかんで接合部全体を引っ張った。試験温度は室温（２５℃）、３００℃ならびに６００℃である。
【００４７】
評価結果を表１に合わせて示す。ここで、実施例を「実」、比較例を［比］として示した。
【００４８】
【表１】

【００４９】
実施例１−１〜１−６は本発明の条件である。温度差が所定の範囲にあり、凸状接合部を有する部材に対し、凹状接合部を有する部材が十分広がっているために、金槌で軽く叩いても押し込むことができた。また、室温に戻った場合の収縮量も十分あるため、締め付け量が大きく、十分な接合強度が得られている。また、必要以上には加熱されていないため、外観から判断できる酸化の状況も問題ない。
【００５０】
特に実施例１−２〜１−４を比較すると明らかなように、試験温度上昇とともに接合強度は向上している。これは、先に述べたように、本発明の第一の実施形態の利点であり、内側に線膨張率の大きい鋼材を、外側に線膨張率の小さいＴｉＡｌ基合金を配置したために、温度上昇によって密着力がさらに増加したことに起因する。すなわち、この実施形態は高温で使われる部材に適していることが確認できる。
【００５１】
比較例１−１、１−２は、凸状接合部を有する部材と凹状接合部を有する部材の温度差が所定の値より小さい比較例である。凸状接合部を有する部材に対し、凹状接合部を有する部材が十分広がっていないために、押し込むことはできなかった。次に、比較例１−３、１−４は温度差が所定の値より大きい比較例である。ＴｉＡｌ基合金の加熱温度は１１００℃以上であり、耐熱性が高いＴｉＡｌ基合金といえども酸化が著しいことから、適当ではなかった。
【００５２】
比較例１−５、１−６は、本発明との比較のために行った、ＴｉＡｌ基合金部材どうしの接合である。押し込み後において、当初の温度差による締め付け力は発生するため、室温の引張強度は良好であった。しかしながら、高温においては、通常の焼きばめと同様に強度は低下した。すなわち、本実施形態の最も大きな特徴である、高温において接合強度がさらに向上するという、結果は得られなかった。また、比較例１−７、１−８は鋼材どうしの接合であり、同様に、室温の強度は高いが高温強度は低下していた。
【００５３】
［実施例２］
次に、凸状接合部を有する部材は鋼材を用い、先端の円筒部をねじ底が直径１０ｍｍとなるような、Ｍ１２×Ｐ１．５の雄ねじに長さ５ｍｍ加工した。一方、凹状接合部を有する部材については、ＴｉＡｌ基合金を用い、ねじ山が直径９．９５ｍｍとなるような、Ｍ１２×Ｐ１．５の雌ねじに長さ５ｍｍ加工した。これらの試験片を実施例１と同様の方法で加熱、冷却して温度差を与え、凸型形状部材を回転しながら凹型形状部品に押し込んだ。
【００５４】
接合条件を表２に示す。温度条件は表１の実施例１−２〜１−４と同じとした。接合後の評価内容も実施例１と同じである。評価結果を表２に合わせて示す。
【００５５】
【表２】

【００５６】
実施例２−１〜実施例２−３のいずれの条件とも、対応する冷却・加熱温度とした実施例１−２〜１−４に較べて接合強度は向上しており、接合界面に突起部を設けた効果が認められる。
【００５７】
［実施例３］
本実施例は第二の実施形態に関するものである。凸状接合部５を有する部材としては主にＴｉＡｌ基合金を用い、先端が直径１０ｍｍで高さ６ｍｍの円筒となるような凸形状に加工した。また外周の径は２０ｍｍにそろえた。一方、凹状接合部６を有する部材については、主に鋼材を用い、先端が直径９．５ｍｍで高さ６ｍｍの円筒穴となるような凹形状に加工した。また外周の径は同様に２０ｍｍにそろえた。
【００５８】
これらの試験片を用い、摩擦接合装置によって凸状接合部を有する部材を回転させながら、凹状接合部を有する部材に押し込んだ。また、比較のために、形状は上記と同じままで、ＴｉＡｌ基合金どうし、および鋼材同士の接合も行った。なお、押し込み量は、摩擦接合による面接合の効果を除外して評価するために、凸部の先端が凹部の底につかない程度の約５ｍｍとした。この値は摩擦接合装置によって制御可能であった。
【００５９】
接合条件は表３に示した条件であった。接合後はそのまま放置して冷却し、実施例１と同様の評価を行った。評価結果を表３に合わせて示す。
【００６０】
【表３】

【００６１】
実施例３−１〜実施例３−５は本発明の条件である。回転数が所定の範囲にあり、十分加熱されていることから、鋼材の収縮量が大きくなり、これに伴って十分な接合強度が得られた。また、必要以上には加熱されていないため、外観から判断できる酸化の状況も問題ない。ただし、実施例３−２〜実施例３−４を比較すると分かるように、室温では十分な強度を有しているものの、高温になるほど接合強度が低下している。この理由は、引張試験時に継手全体が高温になると、外側の鋼材の膨張量が内側のＴｉＡｌ基合金より大きくなり、締め付け力が低下するためである。つまり、この実施形態においては、高温になると継手の強度は低下することから、適用範囲は低温の用途が好ましい。
【００６２】
比較例３−１、比較例３−２は回転数が所定の条件より小さい比較例である。押し込み時の温度上昇が不十分であるために、鋼材の収縮量が小さくなり、接合強度が低くなった。
【００６３】
次に、比較例３−３、比較例３−４は回転数が所定の条件より大きい比較例である。押し込み時の温度上昇が大きすぎるため、接合強度に問題はないが、外観の酸化が著しくなり望ましくない結果であった。なお、酸化しているものは外側の鋼材部材であり、この部分の材料特性変化の評価は行っていないが、酸化状況から判断してかなりの焼鈍効果が生じ材料強度は低下しているものと推察される。
【００６４】
比較例３−５は比較のために行った、ＴｉＡｌ合金部材どうしの接合である。同じ線膨張率であることから、冷却後においても締め付け効果が得られないため、引張強度は非常に低かった。また、比較例３−６は鋼材どうしの接合であり、同様に、締め付け効果が無いため、接合強度は低かった。
【００６５】
［実施例４］
本実施例は第三の実施形態に関するものである。実施例１、２と同じ棒材を用いて試験した。凸状接合部７を有する部材はＴｉＡｌ基合金を用い、先端が直径１０ｍｍで高さ６ｍｍの円筒の中央部に高さ１ｍｍとなる三角形の突起部９を設けた。一方、凹状接合部８を有する部材については鋼材を用い、実施例３と同様に先端が直径９．５ｍｍで高さ６ｍｍの円筒穴となるような凹形状に加工した。これらの試験片を用い、実施例３と同様の方法で接合した。接合条件を表４に示す。表３の実施例３−２〜実施例３−４と同じ２５００ｒｐｍで接合した。接合後の評価内容も実施例３と同じである。評価結果を表４に合わせて示す。
【００６６】
【表４】

【００６７】
いずれの条件とも、対応する回転数条件、引張試験温度で行った実施例３−２〜実施例３−４に較べて接合強度は向上しており、凸状接合部を有する部材の中央に突起を設けた効果が認められた。
【００６８】
【発明の効果】
本発明に係るＴｉＡｌ基合金と鋼材の接合方法によれば、溶接等によって直接には接合できない材料どうしであるＴｉＡｌ基合金と鋼材とを、中間材や接ロウ材を使用することなく、強固に接合することができる。この方法は、中間材やロウ材にかかるコストを削減することができ、接合の対象となる部材に煩雑な加工を施す必要もなく、短時間で簡便に実施できるため、全体としてコスト的に有利な方法である。
【００６９】
また、特に第一の実施形態においては、温度上昇とともに接合強度が向上するという、従来の接合では実現し得なかったことが可能となり、タービン部品等の高温部品への適用に適している。
またさらに、ＴｉＡｌ基合金からなるタービンホイールと鋼材からなるシャフトとを本発明に係る方法を使用して接合された小型過給機は、過渡応答特性の向上、タービン入り口温度の高温化および高速回転化を実現し、高い性能を有するものとなる。
【図面の簡単な説明】
【図１】第一の実施形態の方法により接合されたタービンホイールとシャフトとの接合界面の形状を示す断面図である。
【図２】第二の実施形態の方法により接合されたタービンホイールとシャフトとの接合界面の形状を示す断面図である。
【図３】第三の実施形態の方法により接合されたタービンホイールとシャフトとの接合界面の形状を示す断面図である。
【図４】ＴｉＡｌ基合金と鋼材の温度に対する線膨張係数を示すグラフである。
【符号の説明】
１　タービンホイール
２　シャフト
３　凹状接合部
４　凸状接合部
５　凸状接合部
６　凹状接合部
７　凸状接合部
８　凹状接合部
９　突起部[0001]
[Industrial applications]
The present invention relates to a method for joining a TiAl-based alloy and a steel material. In particular, the present invention relates to a method for joining a TiAl-based alloy and a steel material in the production of turbine wheels for small turbochargers for passenger cars and trucks, and large turbochargers for boats, jet engines, industrial gas turbine blades, and the like.
[0002]
[Prior art]
In recent years, interest in environmental issues has increased, and there is a demand for improving the performance of superchargers used for transport machines such as passenger cars, trucks, and ships, and improving the efficiency of jet engines, industrial gas turbines, and the like. One of the important components that govern the performance and efficiency of the above products is a turbine. In recent years, this turbine has been required to have an improved transient response characteristic, a higher turbine inlet temperature, a higher rotation speed, and the like.
[0003]
As a promising material for improving these performances, an alloy containing an intermetallic compound TiAl as a main phase, which is lighter, has a smaller moment of inertia, and has a higher high-temperature strength than a conventionally used Ni-based superalloy (in the present specification) Then, there is a TiAl-based alloy). Therefore, a gas turbine or the like in which a TiAl-based alloy is used as a turbine wheel, a steel material having toughness and easy to process is used as a shaft, and these are joined is preferably used.
[0004]
However, in order to manufacture such a turbine, it is necessary to join a turbine wheel made of a TiAl-based alloy and a steel shaft. Since the TiAl-based alloy and the steel material cannot be directly joined by welding or the like, a technique for joining the turbine wheel to a steel shaft is important.
[0005]
JP-A-2-157403 discloses that an intermediate material is provided between a turbine wheel made of a TiAl-based alloy and a shaft made of a steel material, and the joining of the TiAl-based alloy and the intermediate material is performed by friction welding, and the joining of the intermediate material and the shaft is performed. Has proposed a joining method performed by electron beam welding. In this method, Incoloy 909 (trade name) or the like having good bondability with a TiAl-based alloy is used as an intermediate material. However, this method requires an intermediate material in addition to the member to be joined, and requires machining of each of the TiAl-based alloy and the intermediate material, and thus has a problem that the joining cost is high.
[0006]
Japanese Patent Application Laid-Open No. 2000-202683 discloses a method of joining a TiAl-based alloy and steel using brazing as joining means. In such a method, a joining surface is formed not only in a surface perpendicular to the axial direction but also in a circumferential direction, and a low-strength brazing material is used for a joining surface in a circumferential direction, which is generated during solidification due to plastic deformation of the brazing material itself. This is to alleviate the stress that occurs. At this time, since this stress is not applied to the joint surface perpendicular to the axial direction, in consideration of the specification of the joint exposed to high temperature for a long time, we provide a joint structure using high-strength brazing material to maintain durability are doing. However, also in this method, the material cost is also required for the brazing itself, and the brazing must be performed under vacuum, so that there is a problem that the joining cost is high.
[0007]
[Problems to be solved by the invention]
It is an object of the present invention to provide a low-cost and simple method for joining a TiAl-based alloy capable of improving transient response characteristics of a small turbocharger and the like, increasing a turbine inlet temperature and increasing a rotation speed, and a steel material. . It is another object of the present invention to provide a bonding method which is suitable for use at a high temperature and has excellent high-temperature strength.
[0008]
[Means for Solving the Problems]
The present invention has been made in order to solve the above-described problems, and is to heat a TiAl-based alloy member provided with a concave joint or to cool a steel member provided with a convex joint. And / or performing both of them to provide a temperature difference between the TiAl-based alloy member and the steel member, and to push the convex joint into the concave joint. It also provides a method for joining steel and steel. It is preferable that the temperature difference is 400 to 1200 ° C. After the pushing, the heated or cooled member is returned to room temperature, so that the members are joined.
[0009]
Joining here is not so-called metallurgical joining in which the components of the materials forming the convex joint and the concave joint are mixed, but rather, the convex joint and the concave joint using heat shrinkage. Is a mechanical joining in which the interface of the two is tightly fixed.
[0010]
It is further preferable that a protrusion is provided in the convex joint, and a groove is provided in the concave joint so as to fit into the protrusion.
[0011]
The method further includes a step of relatively rotating the steel member provided with the concave joint and the TiAl-based alloy member provided with the convex joint to push the convex joint into the concave joint. This is a method for joining a TiAl-based alloy and a steel material. Preferably, the rotation is from 2000 to 3000 rpm. After being pushed in, the members heated by the friction of rotation are returned to room temperature to be in a joined state.
[0012]
It is further preferable that a protrusion is provided on the convex joint.
[0013]
In the method for joining a TiAl-based alloy and a steel material according to the present invention, it is preferable that the TiAl-based alloy member is a turbine wheel of a turbine, and the steel member is a turbine shaft. Here, the turbine includes a supercharger, a jet engine, and an industrial gas turbine used for transportation machines such as passenger cars, trucks, and ships.
[0014]
According to the present invention, since a very brittle phase is generated when mixing of components between materials occurs, a TiAl-based alloy and a steel material, which cannot be directly joined, require a separate intermediate material. Instead, joining can be performed by utilizing the difference between the linear expansion coefficients of the two materials. In such a method, by adjusting the shape of the joint and the joining conditions in accordance with the environment where the joint is placed during operation, joining with high strength is enabled without loosening during operation. Further, in addition to the two members to be joined, there is provided a joining method which can be realized simply and at low cost without requiring additional members as in the prior art and without requiring complicated processing of the joining portion. .
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to embodiments. The same members are denoted by the same reference numerals.
[0016]
The method for joining a TiAl-based alloy and a steel material according to the first embodiment of the present invention is to heat a TiAl-based alloy member provided with a concave joint or to cool a steel member provided with a convex joint. Or a step of giving a temperature difference to both members by performing both of them, and a step of pushing the convex joint into the concave joint.
[0017]
FIG. 1 shows a cross section of a turbine wheel and a shaft joined by the method of the first embodiment. The turbine wheel 1 made of a TiAl-based alloy has a concave joint 3 at an end on the side to be joined. The shaft 2 made of a steel material has a convex joint 4 at the end to be joined.
[0018]
Here, the TiAl-based alloy is an alloy containing Ti as a main constituent element, containing 28 to 35% by weight of Al, and further containing additional elements such as Nb, Cr, Mn, Si, W, C, and B. It is. The steel material is an alloy that contains iron as a main constituent element and may additionally contain additional elements such as C, Cr, Mn, Si, Ni, S, and B.
[0019]
The concave joint portion 3 and the convex joint portion 4 are pre-processed to a size such that they are firmly joined when the temperature returns to room temperature after being pushed. That is, the convex joint 4 is processed so as to be slightly larger than the concave joint 3. However, in this embodiment, since the convex joint 4 is not pushed in while being plastically deformed, it is necessary that the convex joint 4 can be inserted into the concave joint 3 only by lightly tapping with a hammer or the like. That is, at the time of pushing, the concave joint 3 needs to be larger than the convex joint 4.
[0020]
In order to reverse the relationship between the sizes of the two joints at the time of pushing and after returning to normal temperature, at the time of pushing, the TiAl-based alloy member provided with the concave joint 3 is replaced with the convex joint 4. It is necessary to give a predetermined temperature difference to make the temperature higher than that of the steel member provided with.
[0021]
Here, the linear expansion coefficient at a certain temperature differs between the TiAl-based alloy and the steel material. FIG. 4 shows the relationship between the linear expansion coefficient of the TiAl-based alloy and the steel material. When actually processing the convex joint 4 and the concave joint 3, the sizes of the convex joint 4 and the concave joint 3 and the temperature are calculated from the size of the member and the graph of FIG. 4. It is preferable to determine. For example, first, at the time of processing the member at room temperature, the processing is performed such that the convex joint 4 having a diameter of 0.05 mm is larger than the concave joint 3.
[0022]
Next, by heating the TiAl-based alloy member, the concave joint 3 is enlarged by expansion, or by cooling the steel member, the convex joint 4 is reduced by contraction, and the expansion amount of the concave joint 3 and the convexity are reduced. If the value obtained by adding the amount of contraction of the convex joint 4 is 0.1 mm, the concave joint becomes larger by 0.05 mm at the time of pushing, so that it can be easily pushed by hitting with a hammer or the like.
[0023]
When the temperature returns to the normal temperature after the pressing, the size of the member returns to the original size. Therefore, the convex bonding portion 4 becomes 0.05 mm larger than the concave bonding portion 3, and the interface comes into close contact. That is, it can be firmly joined.
[0024]
In the first embodiment, it is desirable that the temperature difference between the two members at the time of pushing is 400 to 1200 ° C. At a temperature of 400 ° C. or lower, the concave joint 3 is not sufficiently larger than the convex joint 4 and cannot be pushed in with a hammer. Further, in order to set the temperature to 1200 ° C. or higher, the TiAl-based alloy must be heated to 1050 ° C. or higher even when the steel member is cooled. In this case, even a TiAl-based alloy having high heat resistance is not desirable because the amount of oxidation increases and the material strength decreases due to the annealing effect. After being pushed in, it is allowed to return to room temperature by leaving it as it is, so that it can be in a strongly bonded state.
[0025]
The contents described above are apparently the same as ordinary shrink fits that have been generally performed, but the effects described below are obtained only by the combination of the TiAl-based alloy and the steel member. The point found is the focus of the present invention.
[0026]
In the method according to the first embodiment, the convex joint 4 is provided with a protruding protrusion, and the concave joint 3 is provided with a groove that fits into the protruding protrusion. Bonding can be performed by providing a temperature difference between the two members in the same manner as described in the embodiment. In the state where the projections and the grooves are present, they cannot be pushed in by simply hitting from above after heating because they become resistance. Therefore, it is necessary to process the protrusion and the groove so as to have a relationship of a male screw and a female screw, and to push in while rotating.
[0027]
By providing such a protrusion and a groove, the area of the interface that is in close contact after joining is increased, and the resistance is increased by the protrusion and the groove when pulled. It becomes difficult for the joint 3 to come off. That is, the joining strength is improved. Furthermore, since rotating parts such as turbines generally rotate in only one direction, if the relationship between the threads of the projections and the grooves is reverse-threaded with respect to the rotation, the effect of the joints during use can be reduced by the effect. Properties can be further improved.
[0028]
Since a TiAl-based alloy member used for a small turbocharger or the like is generally used at a high temperature, the temperature of the joint with the shaft also increases. In the first embodiment, after joining, a steel member having a large linear expansion coefficient is disposed inside, and a TiAl base member having a small linear expansion coefficient is disposed outside, so that it is particularly suitable for use at high temperatures. I have. That is, when the temperature of the joint is increased, the amount of expansion of the internal steel member is larger than that of the external TiAl-based member, so that the joint interface is further pressed, and the adhesion is improved and the joint strength is improved. I do. That is, the fact that the joining strength is improved with increasing temperature, which cannot normally occur, occurs at the joint between the TiAl-based alloy member and the steel member in the present embodiment, and therefore, it is advantageous to perform the joining according to such an embodiment. is there.
[0029]
Next, a second embodiment of the present invention will be described. The method of joining a TiAl-based alloy and a steel material according to the second embodiment is performed by relatively rotating a steel member provided with a concave joint and a TiAl-based alloy member provided with a convex joint. Pushing the convex joint into the concave joint.
[0030]
FIG. 2 is a cross-sectional view illustrating a shape of a joint interface between a turbine wheel and a shaft joined by the method of the second embodiment. The turbine wheel 1 is made of a TiAl-based alloy, and has a convex joint 5 at an end on the side to be joined. The shaft 2 is made of a steel material and has a concave joint 6 at the end on the side to be joined.
[0031]
The convex joint 5 of the turbine wheel 1 and the concave joint 6 of the shaft 2 are processed in advance so that the tip of the convex joint 5 is slightly larger than the hole of the concave joint 6. In this embodiment, frictional heat is generated by pushing the convex joint 5 while rotating it, so that both the convex joint 5 and the concave joint 6 can be pushed in a heated state. Further, after the joining, the interface between the convex joining portion 5 and the concave joining portion 6 comes into close contact due to thermal shrinkage when returning to room temperature, so that the joining portion is firmly fixed.
[0032]
Here, from the graph shown in FIG. 4, since the linear expansion coefficient of the steel material is larger than the linear expansion coefficient of the TiAl-based alloy, in the cooling process after indentation, the contraction amount of the outer steel material is larger than that of the inner TiAl-based alloy. Since it becomes larger than the amount of shrinkage of the alloy and is tightened from the outside, the interface is tightly bonded to the interface.
[0033]
In the second embodiment, the convex joint 5 needs to be larger than the concave joint 6, but the accuracy of the size is not important. In other words, the TiAl-based alloy, which is hard and has high high-temperature strength, which forms the convex joint 5, is forcibly pressed into the soft, low-temperature steel, which forms the concave joint 6, while being relatively rotated. This is because, since plastic deformation of the steel material occurs, even if the concave joint portion is somewhat narrow, it can be expanded.
[0034]
As described above, the second embodiment of the present invention is a joining method that cannot be realized with ordinary metal materials, and is a material having completely different high-temperature strength and linear expansion coefficient, such as TiAl-based alloy and steel. This is a joining method that can be realized only by the combination of the above, and the point that this is found is the main subject of the present invention.
[0035]
In other words, since ordinary metal materials have similar high-temperature strength, even when pressed while rotating, only the concave joint 6 is plastically deformed and the convex joint 5 enters while maintaining its shape. Such an effect cannot be obtained. In addition, even after cooling down to room temperature after the pushing, the shrinkage of the outer and inner members is the same, so that no tightening force is generated, so that the interface does not adhere to each other and a strong bonding force cannot be obtained.
[0036]
The step of pushing the convex joint 5 into the concave joint 6 by relatively rotating the shaft 2 and the turbine wheel 1 includes fixing the shaft 2 and turning the turbine wheel 1 into a device that provides rotation. It can be fitted and screwed into the concave joint 6 while rotating the convex joint 5. However, in the method according to the present invention, since it is only necessary to push in such that it rotates relatively, the same effect can be obtained by rotating the shaft 2 and fixing the turbine wheel 1.
[0037]
The rotation speed is preferably set to 2000 to 3000 rpm. If it is less than 2000 rpm, heating by friction is insufficient, and after cooling, it is not possible to bring about a temperature rise necessary to generate a sufficient tightening force. At 3000 rpm or more, the temperature rises excessively, and particularly a steel member having low heat resistance is notably oxidized, and the material strength is lowered by the annealing action, which is not desirable. The time required for pushing the convex joint 5 into the concave joint 6 while rotating the turbine wheel 1 under the above-described conditions is usually 20 to 30 seconds.
[0038]
According to the method according to the second embodiment, since a normal friction welding device can be used, it is simple and does not cost much. Furthermore, since strictness of processing accuracy of the convex joint 5 and the concave joint 6 is not required, it is advantageous also in the stage of processing the shaft 2 and the turbine wheel 1.
[0039]
The method for joining a TiAl-based alloy and a steel material according to the third embodiment is characterized in that, in the method according to the second embodiment, a projection is provided at a convex joint.
[0040]
FIG. 3 is a cross-sectional view showing a state in which the turbine wheel 1 and the shaft 2 are joined by the rotating and pushing method shown in the third embodiment. At the stage of member processing before joining, the projecting joint 7 provided on the turbine wheel 1 is provided with a protruding projection 9. The shape of the protrusion 9 may be an angled shape or a shape having a curved surface. Further, a plurality of minute projections 9 may be provided. At this point, it is not necessary to form a groove for the concave joint 8 of the steel member, and the concave joint 8 may have the same shape as that of the second embodiment.
[0041]
The joining of these members is performed in the same manner as described in the second embodiment. At the time of pushing, the projection 9 of the convex joint 7 of the TiAl-based alloy which is hard and has high strength at high temperature is not deformed, and the initial shape is maintained. However, the concave joint 8 of the soft and low-temperature steel member is plastically deformed. Occurs. Since this plastic deformation has a shape corresponding to the protrusion 9 of the convex joint 7, it finally has a shape of a groove. The provision of the projection 9 increases the area of the interface that is in intimate contact after bonding, and increases the resistance when pulled by the projection 9 and the groove formed by the projection. The portion 7 and the concave joint 8 are less likely to come off. That is, the joining strength is improved.
[0042]
【Example】
Hereinafter, examples of the present invention will be described. Such examples do not limit the invention.
[0043]
[Example 1]
This example relates to the first embodiment. A test was performed using a TiAl-based alloy bar having a diameter of 25 mm and a steel bar having a diameter of 25 mm. The component of the TiAl-based alloy is Ti-31.3% by weight, Al-7.0% by weight, Nb-1.3% by weight, Cr, which has been subjected to HIP processing at 1250 ° C. to eliminate casting defects after precision casting. It is. On the other hand, the steel member is a free-cutting sulfur steel (standard: AISI-C1144) whose component is Fe-0.45% by weight C-1.5% by weight Mn-0.3% by weight S.
[0044]
The member having the convex joint 4 was mainly made of steel, and was processed into a convex shape having a tip with a diameter of 10 mm and a height of 5 mm. In addition, the diameter of the outer periphery was adjusted to 20 mm. On the other hand, the member having the concave joint portion 3 was mainly processed using a TiAl-based alloy, and was processed into a concave shape such that the tip became a cylindrical hole having a diameter of 9.95 mm and a height of 5 mm. The diameter of the outer circumference was similarly set to 20 mm. Further, for comparison, tests were performed on TiAl-based alloys and steels with the same shape as above.
[0045]
After heating these test pieces in an electric furnace or cooling in liquid nitrogen, the member having a convex joint is lightly tapped with a hammer while being placed on the member having a concave joint, Pushed in on what is possible. The pushing amount was 5 mm at the maximum when the tip of the convex portion was attached to the bottom surface of the concave portion.
[0046]
The joining conditions are the conditions shown in Table 1. The content of the evaluation was, first, whether or not it could be pushed in with a hammer. The pushed-in product was left to cool as it was, and was removed from the joining apparatus after the temperature reached around room temperature. As the evaluation of the joining member thus obtained, a visual observation of the appearance and a joint tensile test were performed. In the joint pulling test, a screw was cut on the outer peripheral portions of both members away from the joint, and the screw was grasped to pull the entire joint. The test temperatures are room temperature (25 ° C), 300 ° C and 600 ° C.
[0047]
The evaluation results are shown in Table 1. Here, the examples are shown as "actual" and the comparative examples as "ratio".
[0048]
[Table 1]

[0049]
Examples 1-1 to 1-6 are the conditions of the present invention. The temperature difference was within a predetermined range, and the member having the concave joint was sufficiently widened with respect to the member having the convex joint. In addition, since there is a sufficient amount of shrinkage when the temperature returns to room temperature, the amount of tightening is large, and sufficient bonding strength is obtained. Further, since the heating is not performed more than necessary, there is no problem in the state of oxidation that can be determined from the appearance.
[0050]
In particular, as is apparent from a comparison of Examples 1-2 to 1-4, the bonding strength is improved as the test temperature increases. As described above, this is an advantage of the first embodiment of the present invention, in which a steel material having a high linear expansion coefficient is disposed on the inside and a TiAl-based alloy having a low linear expansion coefficient is disposed on the outside, so that the temperature rise is increased. This is due to the further increase in adhesion. That is, it can be confirmed that this embodiment is suitable for a member used at a high temperature.
[0051]
Comparative examples 1-1 and 1-2 are comparative examples in which the temperature difference between a member having a convex joint and a member having a concave joint is smaller than a predetermined value. Since the member having the concave joint was not sufficiently spread with respect to the member having the convex joint, the member could not be pushed. Next, Comparative Examples 1-3 and 1-4 are Comparative Examples in which the temperature difference is larger than a predetermined value. The heating temperature of the TiAl-based alloy was 1100 ° C. or higher, and even a TiAl-based alloy having a high heat resistance was not suitable because it was significantly oxidized.
[0052]
Comparative Examples 1-5 and 1-6 are joints of TiAl-based alloy members performed for comparison with the present invention. After the indentation, a tightening force was generated due to the initial temperature difference, so that the tensile strength at room temperature was good. However, at high temperatures, the strength was reduced as in a normal shrink fit. That is, no result was obtained, which is the most significant feature of this embodiment, that the bonding strength is further improved at high temperatures. In Comparative Examples 1-7 and 1-8, the steel materials were joined to each other, and similarly, the strength at room temperature was high but the strength at high temperatures was low.
[0053]
[Example 2]
Next, a steel member was used as the member having the convex joint portion, and the cylindrical portion at the tip was machined into an M12 × P1.5 male screw with a length of 5 mm so that the screw bottom had a diameter of 10 mm. On the other hand, for the member having the concave joint, a female thread of M12 × P1.5 having a length of 9.95 mm and a length of 5 mm was formed using a TiAl-based alloy. These test pieces were heated and cooled in the same manner as in Example 1 to give a temperature difference, and the convex shaped members were pressed into the concave shaped parts while rotating.
[0054]
Table 2 shows the joining conditions. The temperature conditions were the same as in Examples 1-2 to 1-4 in Table 1. The evaluation contents after the joining are the same as those in the first embodiment. The evaluation results are shown in Table 2.
[0055]
[Table 2]

[0056]
In any of the conditions of Examples 2-1 to 2-3, the bonding strength is improved as compared with Examples 1-2 to 1-4 in which the corresponding cooling and heating temperatures are set, and the protrusions are formed at the bonding interface. The effect of providing is recognized.
[0057]
[Example 3]
This example relates to the second embodiment. As the member having the convex joint portion 5, a TiAl-based alloy was mainly used, and was processed into a convex shape having a tip having a diameter of 10 mm and a height of 6 mm. In addition, the diameter of the outer periphery was adjusted to 20 mm. On the other hand, the member having the concave joint 6 was mainly made of a steel material, and was processed into a concave shape such that the tip became a cylindrical hole having a diameter of 9.5 mm and a height of 6 mm. The diameter of the outer circumference was similarly set to 20 mm.
[0058]
Using these test pieces, a member having a convex joint was rotated and pressed into a member having a concave joint by a friction welding device. For comparison, joining was performed between TiAl-based alloys and steel materials while maintaining the same shape as above. In addition, in order to exclude the effect of the surface joining by friction joining and to evaluate it, the indentation amount was set to about 5 mm so that the tip of the projection did not touch the bottom of the recess. This value could be controlled by the friction welding device.
[0059]
The joining conditions were as shown in Table 3. After the joining, it was allowed to cool as it was, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 3.
[0060]
[Table 3]

[0061]
Examples 3-1 to 3-5 are the conditions of the present invention. Since the number of rotations was within a predetermined range and was sufficiently heated, the amount of shrinkage of the steel material increased, and accordingly, sufficient bonding strength was obtained. Further, since the heating is not performed more than necessary, there is no problem in the state of oxidation that can be determined from the appearance. However, as can be seen from a comparison of Example 3-2 to Example 3-4, although having sufficient strength at room temperature, the bonding strength decreases as the temperature increases. The reason for this is that when the temperature of the entire joint becomes high during the tensile test, the amount of expansion of the outer steel material becomes larger than that of the inner TiAl-based alloy, and the tightening force decreases. That is, in this embodiment, since the strength of the joint decreases at high temperatures, the application range is preferably low-temperature applications.
[0062]
Comparative examples 3-1 and 3-2 are comparative examples in which the rotation speed is lower than a predetermined condition. Since the temperature rise during indentation was insufficient, the amount of shrinkage of the steel material was reduced, and the bonding strength was lowered.
[0063]
Next, Comparative Examples 3-3 and 3-4 are Comparative Examples in which the rotational speed is higher than a predetermined condition. Since the temperature rise at the time of indentation was too large, there was no problem in the bonding strength, but the appearance was significantly oxidized, which was an undesirable result. The oxidized material is the outer steel member, and the material property change of this part has not been evaluated.However, judging from the oxidation state, a considerable annealing effect has occurred and the material strength has decreased. Inferred.
[0064]
Comparative Example 3-5 is a joining of TiAl alloy members performed for comparison. Since the same coefficient of linear expansion was used, no tightening effect was obtained even after cooling, so that the tensile strength was very low. Comparative Example 3-6 was a joint between steel materials. Similarly, since there was no tightening effect, the joint strength was low.
[0065]
[Example 4]
This example relates to the third embodiment. A test was performed using the same bar as in Examples 1 and 2. The member having the convex joint 7 was made of a TiAl-based alloy, and a triangular protrusion 9 having a height of 1 mm was provided at the center of a cylinder having a tip of 10 mm in diameter and 6 mm in height. On the other hand, the member having the concave joint 8 was made of a steel material and processed into a concave shape such that the tip became a cylindrical hole having a diameter of 9.5 mm and a height of 6 mm as in Example 3. Using these test pieces, they were joined in the same manner as in Example 3. Table 4 shows the joining conditions. It joined at 2500 rpm same as Example 3-2 of Example 3-Example 3-4. The details of the evaluation after joining are the same as those in the third embodiment. The evaluation results are shown in Table 4.
[0066]
[Table 4]

[0067]
In any of the conditions, the bonding strength is improved as compared with Examples 3-2 to 3-4 performed at the corresponding rotation speed conditions and the tensile test temperature, and a protrusion is provided at the center of the member having the convex bonding portion. The effect of providing was recognized.
[0068]
【The invention's effect】
According to the method for joining a TiAl-based alloy and a steel material according to the present invention, a TiAl-based alloy and a steel material, which are materials that cannot be directly joined by welding or the like, can be firmly bonded without using an intermediate material or a brazing material. Can be joined. This method can reduce the cost of the intermediate material and the brazing material, does not need to perform complicated processing on the members to be joined, and can be easily performed in a short time. Is a great way.
[0069]
Further, in the first embodiment, in particular, it is possible to improve the joining strength with increasing temperature, which is not possible with the conventional joining, and it is suitable for application to high-temperature parts such as turbine parts.
Still further, a small turbocharger in which a turbine wheel made of a TiAl-based alloy and a shaft made of a steel material are joined by using the method according to the present invention has improved transient response characteristics, increased turbine inlet temperature, and high-speed rotation. And achieve high performance.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a shape of a joint interface between a turbine wheel and a shaft joined by a method according to a first embodiment.
FIG. 2 is a cross-sectional view illustrating a shape of a joint interface between a turbine wheel and a shaft joined by a method according to a second embodiment.
FIG. 3 is a cross-sectional view illustrating a shape of a joint interface between a turbine wheel and a shaft joined by a method according to a third embodiment.
FIG. 4 is a graph showing a linear expansion coefficient with respect to a temperature of a TiAl-based alloy and a steel material.
[Explanation of symbols]
1 Turbine wheel
2 shaft
3 Concave joint
4 Convex joint
5 Convex joint
6 Concave joint
7 Convex joint
8 Concave joint
9 Projection

Claims (7)

凹状接合部が設けられたＴｉＡｌ基合金部材を加熱することにより、あるいは、凸状接合部が設けられた鋼材部材を冷却することにより、あるいはこれらの両方を行うことにより、該ＴｉＡｌ基合金部材と該鋼材部材とに温度差を与えるステップと、
該凸状接合部を、該凹状接合部に押し込むステップと
を含むＴｉＡｌ基合金と鋼材の接合方法。By heating the TiAl-based alloy member provided with the concave joint, or by cooling the steel member provided with the convex joint, or by performing both of these, the TiAl-based alloy member and Giving a temperature difference to the steel member;
Pushing the convex joint into the concave joint. 前記温度差が４００〜１２００℃である請求項１に記載の方法。The method according to claim 1, wherein the temperature difference is between 400 and 1200C. 前記凸状接合部に突起部を設け、該突起部に嵌合するように前記凹状結合部に溝部を設けることを特徴とする請求項１または２に記載の方法。The method according to claim 1, wherein a protrusion is provided in the convex joint, and a groove is provided in the concave joint so as to fit in the protrusion. 凹状接合部が設けられた鋼材部材と凸状接合部が設けられたＴｉＡｌ基合金部材とを相対的に回転させることにより、該凸状接合部を、該凹状接合部に押し込むステップを含むＴｉＡｌ基合金と鋼材の接合方法。Pressing the convex joint into the concave joint by relatively rotating the steel member provided with the concave joint and the TiAl-based alloy member provided with the convex joint. How to join alloy and steel. 前記回転が、２０００〜３０００ｒｐｍである請求項４に記載の方法。The method according to claim 4, wherein the rotation is between 2000 and 3000 rpm. 前記凸状接合部に突起部を設けることを特徴とする請求項４または５に記載の方法。The method according to claim 4, wherein a protrusion is provided on the convex joint. 前記ＴｉＡｌ基合金部材がタービンのタービンホイールであり、前記鋼材部材がタービンのシャフトである請求項１〜６のいずれかに記載の方法。The method according to claim 1, wherein the TiAl-based alloy member is a turbine wheel of a turbine, and the steel member is a turbine shaft.

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