JP4219642B2

JP4219642B2 - Friction stir welding method of platinum or platinum-base alloy and its joining structure

Info

Publication number: JP4219642B2
Application number: JP2002255594A
Authority: JP
Inventors: 桂一郎松下; 長治坂井; 孝之島宗
Original assignee: Furuya Metal Co Ltd
Current assignee: Furuya Metal Co Ltd
Priority date: 2002-08-30
Filing date: 2002-08-30
Publication date: 2009-02-04
Anticipated expiration: 2022-08-30
Also published as: JP2004090050A

Description

【０００１】
【発明の属する技術分野】
本発明は、白金又は白金基合金の接合を行なう摩擦攪拌接合法及びその接合構造に関し、溶解用装置、酸化物単結晶育成用ルツボ、蛍光Ｘ線分析用ビート皿、各種パイプ等に用いられる白金合又は白金基合金の接合に適用し得る発明である。
【０００２】
【従来の技術】
従来、白金基合金同士の接合は、ほとんどの製品がＴＩＧ（tungsten inert gas）溶接機やガスバーナーを用いて溶接している。ここで、ＴＩＧ溶接とはトーチから流す大気遮断ガス中で、溶接母材との間にアークのみを発生させる非消耗のタングステン電極を使用し、溶着金属はアーク側面から溶加材を送給して溶融形成させる方法である。この溶接部は母材に対してかなり強度低下する。特にガラス溶解用ルツボ等で使用している酸化物分散型強化白金については、その強度低下率は極めて大きい。母材と溶接部の強度差が大きいと、溶接部に応力が集中してその周辺から破断するケースが多い。
【０００３】
ガラス溶解用装置、酸化物単結晶育成用ルツボ、蛍光Ｘ線分析用ビート皿等に用いられる白金合金製品において、ほとんどの製品は溶接部位が存在する。溶接は主にＴＩＧ溶接機を用いて行っている。しかし、白金合金、特に酸化ジルコニウム（ZrO₂）、酸化カルシウム（CaO）、酸化イットリウム（Y₂O₃）等を含む酸化物分散型強化白金の溶接部位の強度が弱いことから、溶接部周辺でのトラブルが多かった。
【０００４】
そこで従来は、図８に示すように溶接部に肉盛りすることや図９に示すように溶接部周辺に同素材のバンドを補強鍛接することによって強度低下の防止を図っていた。ここで、白金合金製品の肉厚については０．５〜５ｍｍであり、補強バンドの肉厚については０．２〜０．５ｍｍである。
【０００５】
ＴＩＧ溶接やガスバーナーによる溶接の特徴は、比較的作業が容易であること、溶接機が比較的安価に購入できること等が挙げられる。肉盛り溶接やバンドの補強鍛接については、わずかな強度アップしか得られなくても製品の寿命延長に大きく起因するために必要なことであった。
【０００６】
一方、金属の接合方法として例えば特表平７−５０５０９０号公報や特表平９−５０８０７３号公報に摩擦攪拌接合法の技術が開示されている。摩擦攪拌接合（Friction Stir Welding）は、鉄、アルミニウム合金などの金属相互の溶接は勿論異種金属の溶接すら可能な溶接法である。
【０００７】
摩擦攪拌接合については、融点が比較的低いアルミニウム及びアルミニウム合金を対象とした接合が多く検討されているが、白金又は白金基合金を被溶接物として摩擦攪拌接合を適用した報告例はない。
【０００８】
【発明が解決しようとする課題】
摩擦攪拌接合法は、アルミニウム合金等を対象とする場合には多くの知見があるが、白金又は白金基合金等の貴金属に対応する知見や高融点材料に対応した知見は見受けられない。摩擦攪拌接合法を白金又は白金基合金の接合に採用した場合には肉盛りやバンドの必要性がなくなるが、その一方で強度低下の問題には特に注意を払う必要がある。
【０００９】
通常、金属はその表面にガス吸着をしており、そのガス成分が金属と酸化反応等の化学反応を起こして表面に化合物層を形成していることが多い。摩擦攪拌接合の場合、接合領域に吸着ガス分子や前記化合物層が存在しても接合領域に挿入するプローブピンが摩擦熱によって形成された可塑性領域を攪拌するため、可塑性領域全体に吸着ガス分子や前記化合物層が分散される。したがって、加工物の当接面に吸着ガス分子や前記化合物層を集中させたまま接合した場合と比較すると大きな接合強度が得られる。
【００１０】
しかし、白金又は白金基合金の加工では、接合箇所の強度低下が特に問題となるので、可塑性領域全体に吸着ガス分子や前記化合物層を分散させても、充分な接合強度が得られない。
【００１１】
そこで本発明者は、摩擦攪拌接合法を白金又は白金基合金の接合に適用する際に金属表面に吸着した吸着ガス分子を除去する目的で予熱工程を設けること或いはその吸着分子と白金との化合物からなる表面に形成された化合物層を除去する目的で予熱工程を意図的に設けることで、肉盛りやバンドをすることなくしかも強度低下を抑制可能であることを見出して本発明を完成させた。
【００１２】
すなわち本発明の目的は、摩擦攪拌接合法を用いて、白金又は白金基合金からなる加工物同士を接合する場合に際して、結合領域の表面に形成された酸素等の化合物層を除去する予熱工程を設けることで、破損の起点となり得る異物相の混入を排除し、接合部の強度低下を防止することである。ここで、予熱工程における結合領域の最適加熱温度を規定することも目的とする。
【００１３】
また本発明の目的は、摩擦攪拌接合法を用いて、白金又は白金基合金からなる加工物とパラジウム、銅、銀若しくはステンレス或いはこれらの金属基合金からなる加工物とを接合する場合に際して、結合領域の表面に吸着した吸着気体分子を除去させる予熱工程を設けることで、破損の起点となり得るボイドや空孔の混入を排除し、接合部の強度低下を防止することである。パラジウム、銅、銀、ステンレスなどの異種金属と白金又は白金基合金の接合は、例えば通電加熱用電極と白金との接合を強度あるものとし、炉等の安定操業につながるものである。
【００１４】
本発明では、予熱工程を大気雰囲気下で行なうことで、接合作業の容易化、さらには現場での接合作業を可能とすることを目的とする。
【００１５】
また本発明では、結合領域をレーザー照射するという予熱工程における最適な加熱方法を提案することを目的とする。
【００１６】
さらに本発明では、高融点材料である白金又は白金基合金を接合するために摩擦熱を効果的に接合領域に集中させなければならない。そこで、その手段として放熱防止のための断熱方法を提案することを目的とする。
【００１７】
また本発明では、接合領域を摩擦熱によって高温に加熱する必要があるため、プローブピンは、その高温に耐え得る強度を有すること、また白金との反応性がないことが要求される。そこで、使用する最適なプローブピンの材質を提案することを目的とする。
【００１８】
白金又は白金基合金のうち、酸化物分散強化型の白金又は白金基合金では、分散させた酸化物が偏析すると強度低下が激しい。そこで本発明では酸化物分散強化型の白金又は白金基合金を強度低下させることなく接合させる方法を提案する。
【００１９】
本発明の目的は、酸化物分散強化型の白金又は白金基合金の接合において、従来行なわれていた接合方法では得られない接合構造を提供することを目的とする。すなわち、接合部において金属粒子の粗大化が抑制され且つ強化のために分散させた酸化物粒子の偏析が抑制された接合構造を提供する。
【００２０】
本発明は、上記のように接合法を従来の溶接法から予熱工程を有する摩擦攪拌接合法に換えることにより、接合部の強度を大幅に向上させ、従来の製品の寿命延長やコストダウンを行なうものである。
【００２１】
また本発明は、白金又は白金基合金同士の接合のみならず、クラック箇所の修理等にも適用することを目的とする。
【００２２】
【課題を解決するための手段】
本発明に係る白金又は白金基合金の摩擦攪拌接合法は、加工物を相互に当接若しくはほぼ当接させて細長の結合領域を規定する工程、前記加工物の材料よりも硬い材料からなるプローブピンを回転させながら前記結合領域に挿入してプローブピンと結合領域との間で摩擦熱を発生させ、発熱させた結合領域中に可塑性領域を発生させる工程、前記可塑性領域を凝固させて前記加工物同士を接合する工程を備えた摩擦攪拌接合法において、前記加工物を白金又は白金基合金からなる加工物とし、且つ前記可塑性領域を発生させる工程に入る前に予め、前記結合領域の表面に吸着した酸素分子、窒素分子又は水分子等の吸着気体分子の解離温度以上及び前記結合領域の表面に形成された白金又は白金基合金と前記吸着気体分子との化合物層の解離温度以上且つ前記加工物の融点未満に前記結合領域を加熱することで前記結合領域を還元活性化させて、前記吸着気体分子及び前記化合物層を除去する予熱工程を設けることを特徴とする。
【００２３】
本発明に係る白金又は白金基合金の摩擦攪拌接合法では、前記予熱工程において、前記結合領域を５３０〜１６００℃に加熱して、白金又は白金基合金を還元活性化させることが好ましい。
【００２４】
本発明に係る白金又は白金基合金の摩擦攪拌接合法は、加工物を相互に当接若しくはほぼ当接させて細長の結合領域を規定する工程、前記加工物の材料よりも硬い材料からなるプローブピンを回転させながら前記結合領域に挿入してプローブピンと結合領域との間で摩擦熱を発生させ、発熱させた結合領域中に可塑性領域を発生させる工程、前記可塑性領域を凝固させて前記加工物同士を接合する工程を備えた摩擦攪拌接合法において、
前記加工物を白金又は白金基合金からなる加工物とパラジウム、銅、銀若しくはステンレス或いはこれらの金属基合金からなる加工物との組み合わせとし、且つ前記可塑性領域を発生させる工程に入る前に予め、前記結合領域の表面に吸着した酸素分子、窒素分子又は水分子等の吸着気体分子の解離温度以上且つ前記加工物の融点未満に前記結合領域を加熱して、前記吸着気体分子を除去させる予熱工程を設けることを特徴とする。
【００２５】
また、本発明に係る白金又は白金基合金の摩擦攪拌接合法では、前記予熱工程を大気雰囲気下で行なうことが好ましい。
【００２６】
本発明に係る白金又は白金基合金の摩擦攪拌接合法では、前記予熱工程において、前記結合領域にレーザーを照射して加熱することが好ましい。
【００２７】
本発明に係る白金又は白金基合金の摩擦攪拌接合法では、前記プローブピンの挿入方向に対して反対方向から前記結合領域に放熱防止のための断熱材を当てることが好ましい。
【００２８】
また、本発明に係る白金又は白金基合金の摩擦攪拌接合法では、イリジウム或いはロジウム又はそれらの合金で形成したプローブピンを使用するか、或いは耐熱衝撃性を有する、窒化アルミニウム、窒化タンタル、窒化硼素、窒化チタン、窒化ジルコニウム若しくは窒化ハフニウム等の窒化物系化合物又は炭化チタン、炭化ジルコニウム、炭化タンタル、タングステンカーバイト、炭化硼素若しくは炭化ハフニウム等の炭化物系化合物又は酸化ハフニウム、酸化ジルコニウム若しくは酸化クロム等の高融点酸化物又はこれらの混合焼結体を主成分とする材料で形成したプローブピンを使用することが好ましい。
【００２９】
また、本発明に係る白金又は白金基合金の摩擦攪拌接合法では、前記プローブピンの基体を１５００℃以上の高融点金属で形成し、該基体の表面に窒化チタン等の高硬度セラミックスを被膜したプローブピンを使用することが好ましい。
【００３０】
さらに、本発明に係る白金又は白金基合金の摩擦攪拌接合法では、前記の白金又は白金基合金は、酸化物分散強化型の白金又は白金基合金であることが好ましい。
【００３１】
本発明に係る摩擦攪拌接合法により接合した酸化物分散強化型の白金又は白金基合金からなる加工物の接合構造は、可塑性領域の凝固部において、金属粒子又は白金基合金粒子の粗大化が抑制され且つ強化のために分散させた酸化物粒子の偏析が抑制された構造であることを特徴とする。
【００３２】
【発明の実施の形態】
以下、本発明を実施形態及び実施例を示して詳細に説明するが、本発明はこれらの記載に限定して解釈されない。
【００３３】
最初に図１０を参照して摩擦攪拌接合法のプロセスについて説明する。摩擦攪拌接合法は、加工物1A,1Bを相互に当接若しくはほぼ当接させて細長の結合領域２を規定する工程、加工物1A,1Bの材料よりも硬い材料からなるプローブピン３を回転させながら結合領域２に挿入してプローブピン３と結合領域２との間で摩擦熱を発生させ、発熱させた結合領域中に可塑性領域を発生させる工程、プローブピン３を取り外して可塑性領域を凝固させて加工物同士を接合する工程を備えるものである。なお、プローブピン３はモータ７によって回転する。
【００３４】
ここで、プローブピン３はペンシル部分４を備える。プローブピン３と加工物1A,1Bとの摩擦が行なわれなければならないので、加工物1A,1Bは相互に当接されていなければならない。摩擦が行なわれることを条件に加工物がほぼ当接していても良い。また、スポット接合ではなく連続した接合を行なうために結合領域２は細長でなければならず、接合領域に大きな空間があるとプローブピン３と加工物1A,1Bとの摩擦が行なわれない。さらに、プローブピンは摩擦熱に耐えなければならず、且つ回転によるねじれの応力に耐え得る強度を有する必要がある。
【００３５】
次に摩擦攪拌接合法の原理について説明する。加工物1A,1Bを突合せ、プローブピン３を回転させ、ペンシル部分４をゆっくりと結合領域２である突合せラインに押し込む。このペンシル部分４の長さは溶接深さに必要なものとする。プローブピン３が回転して、結合領域２に接触すると摩擦が接触点の材料を急速に加熱させ、その結果材料の機械的強度を低下させる。さらに力を加えるとプローブピン３はその動き８に沿って材料をこね、押し出す。接合領域２では、プローブピン３の回転する円筒形の肩状部とペンシル部分４によって発生した摩擦熱が肩状部の下とペンシル部分の周りの金属に高温の可塑性領域を作る。加工物がプローブピン３の動きと反対方向に動くかその逆に動くと、塑性化した金属はプローブピン３の進行方向の前端で潰れ、機械的攪拌とプローブピン３の形状と回転方向による鍛造作用によって後端へ移動する。この結果、器具の前面の接合部を加熱し、可塑性領域を作り出す。そして加工物に存在する酸化膜を破壊し潰れた金属を攪拌しながら、器具の後端で可塑性領域は冷却されて固体状の溶着を形成するに至る。この現象はすべて被溶接物の融点よりも低い温度で生じる。
【００３６】
摩擦攪拌接合では、亀裂発生がなくなり、溶着金属の蒸発による合金要素のロスが無く、合金成分をそのまま保持でき、さらに溶接器具の圧入、攪拌及び鍛造作用によって微細な粒状組織が溶着金属に形成されるというメリットがある。
【００３７】
次に本発明の白金又は白金基合金の摩擦攪拌接合法について説明する。本発明の第１形態では、加工物1A,1Bは白金又は白金基合金からなる加工物とする。そして、可塑性領域を発生させる工程に入る前に予め、結合領域の表面に吸着した酸素分子、窒素分子又は水分子等の吸着気体分子及び結合領域の表面に形成された酸素等の化合物層の解離温度以上且つ前記加工物の融点未満に結合領域を加熱することで、結合領域を還元活性化させて、吸着気体分子と化合物層を除去する予熱工程を設ける。
【００３８】
ここで、白金基合金は、白金を５０ｗｔ％以上含有している多元合金であり、例えば白金−ジルコニウム合金、白金−イットリウム合金、白金−ロジウム合金、白金−イリジウム合金、白金−ジルコニウム−ロジウム合金、白金−ジルコニウム−金合金等がある。酸化物分散強化型の白金も白金基合金の一種である。
【００３９】
通常、白金又は白金基合金の表面には、空気中の酸素分子、窒素分子及び水分子が吸着している。ここで多くの場合、水分子により表面には酸化層（PtO）等の化合物層が形成される。通常の摩擦攪拌接合では、摩擦熱によって形成された可塑性領域をプローブピンによって攪拌するので吸着ガス分子と酸化層は可塑性領域中に混ぜ込まれて分散する。白金又は白金基合金を加工物とする場合でも同様に吸着ガス分子と化合物層は可塑性領域中に分散混合される。
【００４０】
本発明では、白金又は白金基合金の加工物はガラス溶解坩堝等をはじめとして高温で使用する用途が多い。このような厳しい使用条件下では可塑性領域中に分散混合された吸着ガス分子と化合物層に応力が集中して接合部分の破壊の起点になってしまう。そこで、本発明では可塑性領域を発生させる工程に入る前に、吸着ガス分子や化合物層を予め除去する予熱工程を設けることとした。予熱条件は、結合領域の表面の吸着気体分子、化合物層の解離温度以上且つ加工物の融点未満に前記結合領域を加熱する。前記温度に加熱することで、結合領域の表面に吸着した吸着ガス分子を完全に解離させ、さらにその表面を還元活性化させて化合物層を解離させることができる。
【００４１】
予熱工程における加熱が解離温度未満であればボイドが残存したり、化合物層に起因する不純物が残存する。そこで白金又は白金基合金の場合、５３０℃以上にすれば、酸素含有の雰囲気中においても還元活性化され、表面に形成された酸化層を消失させることが可能である。本発明では還元活性を高めるために、６００℃以上とすることが好ましい。一方、白金の融点はほぼ１７７０℃であり、融点を超えると液化することから、接合領域において融着してしまうか、或いは加工物が融解により形状を維持できなくなってしまう。そこで加熱上限温度を融点以下とし、予熱工程の後で可塑性領域を形成し攪拌する工程を行なうために１６００℃以下で予熱工程を行なうことが好ましい。したがって、予熱工程では、５３０℃以上１６００℃未満に加熱することが好ましく、さらに好ましくは６００℃以上１５００℃以下に加熱する。ここで、６００℃以上１５００℃以下に加熱することにより、予熱工程において白金又は白金基合金を再結晶化させることができる。再結晶化させることで、結晶粒子は軟化し、次工程で可塑性領域を形成した際に攪拌効率を高めることができる。
【００４２】
予熱工程において、結合領域表面にある吸着ガス分子を離脱させ且つ化合物層を完全に除去させるために、加熱は所定時間行なう。加熱温度によって必要な加熱保持時間は異なるが、例えば６００℃に加熱する場合には５〜１０分間加熱保持することが好ましい。５分以下では吸着ガス分子の離脱及び化合物層除去が不十分になると思われ内部欠陥も発生する。また、１０分以上では、作業効率が好ましくなくなる。なお、加熱温度が高いと還元活性を高めることができるため、吸着ガス分子の離脱と化合物層の除去が進み、加熱保持時間を短縮することができる。
【００４３】
なお、必要以上に加熱保持時間が長いと再結晶粒子が二次成長して粒子の粗大化を招く。予熱工程後、プローブピンによって可塑性領域を攪拌するが、攪拌不充分で粗大化した再結晶粒子が残ると強度低下につながるため、加熱保持時間は再結晶粒子の粗大化が生じない程度の時間にする。
【００４４】
本発明の第２形態は、白金又は白金基合金からなる加工物とパラジウム、銅、銀若しくはステンレス或いはこれらの金属基合金からなる加工物との組み合わせの接合を行なうものである。そして、可塑性領域を発生させる工程に入る前に予め、加工物の結合領域表面に吸着した酸素分子、窒素分子又は水分子等の吸着気体分子の解離温度以上且つ前記加工物の融点未満に前記結合領域を加熱して、結合領域の表面に吸着している吸着気体分子を除去させる予熱工程を設ける。
【００４５】
第１形態で説明した通り、白金又は白金基合金の表面には酸素分子、窒素分子又は水分子等の吸着気体分子が吸着しており、白金とは異種金属であるパラジウム、銅、銀若しくはステンレス或いはこれらの金属基合金の表面にも同様の吸着ガス分子が存在する。本発明では接合部分においてこの吸着気体分子の影響による強度低下を防止するために予熱工程を設けることとした。
【００４６】
予熱条件は、吸着気体分子の解離温度以上前記加工物の融点未満に加熱する。吸着には化学吸着と物理吸着の2つがある。吸着される成分が固体表面と化学的な強い結合をする場合を化学吸着と呼び，金属上の酸素や水素等の吸着が例としてあげられる。これは表面での金属と気体との化学反応と考えることができ、吸着時の発熱が大きく、簡単に気体が金属から離れることはない。これに対して、吸着される成分の分子と固体表面の間の物理的な力、すなわちファン・デル・ワールス力などにより吸着が生じる場合を物理吸着といい、この場合の吸着時に発生する熱は、その吸着分子の凝縮熱より若干高い程度である。本発明では、金属表面に化学吸着している酸素や水の除去を行なう必要がある。金属種によって結合力が異なるため解離温度は異なるが、本発明では４００℃以上に加熱する。予熱工程における加熱が解離温度未満であればボイドが残存したり、化合物層に起因する不純物が残存する。
【００４７】
ここで、第１の実施形態と同様に５３０℃以上に加熱すれば、白金又は白金属合金からなる加工物の結合領域表面では、酸素含有の雰囲気中においても還元活性化され、表面に形成された酸化層を消失させることが可能であり、６００℃以上とすれば還元活性を高めることができる。したがって、第２の実施形態では、予熱工程における加熱下限温度は４００℃、好ましくは５３０℃さらに好ましくは６００℃とする。６００℃以上に加熱することにより、予熱工程において加工物の再結晶化をさせることができる。再結晶化させることで、結晶粒子は軟化し、次工程で可塑性領域を形成した際に攪拌効率を高めることができる。
【００４８】
一方、加熱上限温度を融点未満とすることは融着防止若しくは加工物の形状維持のためであることは前述の通りである。加工物の融点は、加工物の融解を防止するために、組み合わせた加工物のうち融点の低い温度を選択する。通常は白金又は白金基合金の融点が高いため、異種金属の融点未満を加熱上限温度とする。パラジウムの融点は１５５４℃、銅の融点は１０８３℃、銀の融点は９６１℃、ステンレスの融点は種類によって異なるが例えばマルテンサイト系ステンレス鋼で１５１０℃である。ただし、融点を超えると液化することから、予熱工程の後で可塑性領域を形成し攪拌する工程を行なうために加熱上限温度は次の通りとすることが好ましい。異種金属がパラジウムの場合は１３００℃以下、銅の場合は８００℃以下、銀の場合は７００℃以下、ステンレスの場合は、例えばマルテンサイト系ステンレス鋼で１２５０℃以下である。
【００４９】
第２の実施形態においても、予熱工程において結合領域表面にある吸着ガス分子を離脱させるために加熱は所定時間行なう。加熱温度によって必要な加熱保持時間は異なるが、例えば６００℃に加熱する場合には５〜１０分間加熱保持することが好ましい。５分以下では吸着ガス分子の離脱不十分になると思われ内部欠陥も発生する。また、１０分以上では、作業効率が好ましくなくなる。ただし、第１の実施形態と同様に加熱保持時間は再結晶粒子の粗大化が生じない程度の時間にする。
【００５０】
第１及び第２の実施形態において、本発明では白金又は白金基合金が５３０℃以上にて還元活性化することを利用して結合領域表面に形成された化合物層を除去するが、この還元活性化は大気雰囲気下でも作用する。したがって、本発明では特別な雰囲気調整は不要であり、現場にて接合作業を行なうこともできるというメリットがある。
【００５１】
予熱工程において、加工物の結合領域における加熱は通電加熱や白金ヒーターによる接合部周囲の加熱、ガスバーナー、プラズマトーチ等を用いて接合部周辺を局部加熱するが、結合領域をスポット的に加熱でき且つ表面に加熱以外の影響を与えないためにレーザーを照射して加熱することが好ましい。この場合のレーザーとしては、YAGレーザー、CO_２レーザーである。
【００５２】
さらに、予熱工程における加熱時にプローブピンの挿入方向に対して反対方向から結合領域に放熱防止のための断熱材を当てることにより、結合領域における温度分布の不均一を是正し、吸着ガス分子の解離、還元活性化をムラなく行なうことが好ましい。断熱材としては、アルミナ等の熱伝導の小さなセラミックスが好ましい。
【００５３】
プローブ材質の選定基準は、接合材より硬い材質で耐摩耗性に優れていること、加工中に割れたり欠けたりしないこと、酸化による消耗や劣化のないこと、接合材と容易に合金をつくらないこと等が挙げられる。従って、酸化アルミニウムや酸化ジルコニウム等のセラミックスについては、加工中での割れや欠けの問題があり、タングステン、タンタル、ニオブ、モリブデン、ルテニウム等の高融点金属については、酸化による消耗や劣化があり、プローブ材質には適さない。そこで本発明では、イリジウム或いはロジウム又はそれらの合金で形成したプローブピンを使用する。イリジウムは融点が２４５７℃、ロジウムは融点が１９６３℃と白金よりも高融点材料である。合金としては、イリジウム基合金、ロジウム基合金、イリジウム−ロジウム合金がある。
【００５４】
またプローブピンとして、耐熱衝撃性を有する、窒化物系化合物、炭化物系化合物、高融点酸化物又はこれらの混合焼結体を主成分とする材料で形成しても良い。窒化物系化合物としては、窒化アルミニウム、窒化タンタル、窒化硼素、窒化チタン、窒化ジルコニウム、窒化ハフニウムが例示でき、炭化物系化合物としては炭化チタン、炭化ジルコニウム、炭化タンタル、タングステンカーバイト、炭化硼素、炭化ハフニウムが例示でき、高融点酸化物としては酸化ハフニウム、酸化ジルコニウム、酸化クロムが例示できる。これはいずれも白金よりも高融点で耐熱衝撃性を有する。
【００５５】
さらにプローブピンとして、プローブピンの基体を１５００℃以上の高融点金属で形成し、基体の表面に窒化チタン等の高硬度セラミックスを被膜したプローブピンを使用してもよい。高融点金属としては、タングステン、タンタル、モリブデン、イリジウム等が例示できる。
【００５６】
本発明においては、予熱工程において上記説明したような加熱温度及び加熱時間を遵守することで、吸着ガス分子と結合領域表面の化合物層を除去し且つ再結晶粒子の粗大化を防止しつつ接合を行なうため、酸化物分散強化型の白金又は白金基合金からなる加工物の接合構造は、可塑性領域の凝固部において、金属粒子の粗大化が抑制され且つ強化のために分散させた酸化物粒子の偏析が抑制された構造となる。ＴＩＧ溶接機やガスバーナーを用いて溶接した接合構造は、白金の結晶粒子が粗大化し、且つ粒界に強化のために分散させた酸化物粒子が偏析してしまう構造となり、溶接部分以外と比較すると極端に強度低下している。これに対して本発明の接合構造は、粒子の粗大化防止と酸化物粒子の偏析防止を実現し、接合部での強度低下を防止した。
【００５７】
加工物の厚さは１〜３mm、プローブピンのシャフト径は、直径８〜１２ｍｍ、プローブピンのペンシル部分の直径は１〜３mm、プローブピンのペンシル部分の長さは加工物の厚さによるがおおよそ０．７〜２．７ｍｍ、プローブピンの回転速度は５００〜１５００ｒｐｍ、プローブピンの移動速度は、２０〜５０ｍｍ／ｓが例示できる。また、可塑性領域を作り出すためにプローブピンの摩擦熱による加熱は、白金又は白金基合金同士の接合の場合は１２００〜１５００℃とし、異種金属と白金又は白金基合金同士の接合の場合は５００〜１４００℃とし、異なる加工物を接合する場合には低い方の融点未満までとする。
【００５８】
【実施例】
以下、実施例を示す。
（実施例１）
加工物の材質はZrO₂を０．１６ｗｔ％添加した酸化物分散型強化白金とし、同種の加工物の接合を大気雰囲気中で行なった。加工物は板材であり、板材の肉厚は２ｍｍのものを用いた。プローブピンの材質はイリジウムとした。プローブピンのシャフト径は直径１０ｍｍ、プローブピンの直径は１．５mm、ペンシル部分の長さは１．７mmとした。加工物の側部を突合せて結合領域を規定し、プローブピンの挿入方向に対して反対方向から結合領域に放熱防止のための断熱材として、アルミナを当てた。次に予熱工程に入った、白金ヒーターにより結合領域周囲を加熱した。加熱温度は６００℃とし、１０分間加熱保持した。予熱工程を終えて、次に可塑性領域を形成する工程に入る。プローブピンを回転速度８００ｒｐｍで回転し、結合領域に挿入した。可塑性領域が形成された後、プローブピンを結合領域のラインに沿って移動させた。このときの移動速度は３０ｍｍ／ｓとした。摩擦熱により、接合部温度は１３００〜１４００℃に達した。プローブピンで走査し終えた可塑性領域は自然冷却と共に凝固した。結合領域を全てプローブピンで走査した後、プローブピンを回転させたまま加工物から引き抜いた。これにより、２つの加工物が接合された。この接合部分の接合強度を調べるために高温クリープ特性を高温クリープ炉（自社製）を用いて測定した。結果を図１に示す。なお、測定条件は、大気雰囲気、１５００℃で測定を行なった。母材強度に対して９０％以上の強度が得られた。また、図２に接合部分の断面構造の金属組織を示す顕微鏡画像を示した。ここで、加工物断面の組織は母材組織であり、中央部分が溶接部分の組織である（以下、断面構造の金属組織を示す顕微鏡画像において同じ）。結晶のサイズが母材よりは大きいものの非常に細かく、結晶粒子の成長が抑制されていた。また、結晶自体にうねりを生じている。接合部分内の組成について、酸化物の濃度は０．１５ｗｔ％であり、母材の酸化物の濃度である０．１６ｗｔ％とそれ程差異はなく、分散させた酸化物の偏析もみられなかった。さらに、プローブピンの挿入方向から見た接合後の加工物の表面の顕微鏡画像を図３に、加工物の裏面の顕微鏡画像を図４に示した。
【００５９】
（実施例２）
予熱工程における加熱方法としてレーザー（ダイヘン社、APELIO ２５１０V）を用いた以外は実施例１と同様に接合を行なった。実施例１と同様の結果が得られ、強度低下せずに接合できることが確認された。
【００６０】
（実施例３）
予熱工程における加熱温度を１２００℃、５分間加熱保持した以外は実施例２と同様の条件で接合を行なった。可塑性領域の形成の際にプローブピンの摩擦熱により、接合部温度は１３００〜１４００℃に達した。実施例１と同様に母材強度に対して９０％以上の強度が得られた。また、接合部分の断面構造の金属組織は図２と類似しており、結晶サイズが非常に細かく、結晶粒子の成長が抑制されていて、結晶自体にうねりを生じていた。接合部分内の組成について、酸化物の濃度は０．１５ｗｔ％であり、母材の酸化物の濃度である０．１６ｗｔ％とそれ程差異はなく、分散させた酸化物の偏析もみられなかった。
【００６１】
（実施例４）
加工物の材質は、一方をZrO₂０．１６ｗｔ％添加した酸化物分散型強化白金とし、他方をパラジウムとし、異種の加工物の接合を大気雰囲気中で行なった。加工物は共に板材であり、板材の肉厚は２ｍｍのものを用いた。プローブピンの材質はイリジウムとした。それ以外の条件は実施例１と同様に行なった。摩擦熱により、接合部温度は１３００〜１４００℃に達し、可塑領域が凝固して２つの加工物が接合された。接合強度はＴＩＧによりこれらの加工物を接合した場合と比較して２．０倍であった。
【００６２】
（比較例１）
実施例１と同じ加工物をＴＩＧ溶接により突合接合を行ない、比較例１とした。実施例１と同様に高温クリープ特性を調べ、結果を図１に示した。溶接部の強度は母材強度の３０〜４０％であった。また図５に接合部分の断面構造の金属組織を示す概念図を示した。図５に示す様にＴＩＧ溶接品は結晶のサイズが大きく、結晶粒子が成長していた。接合部内の組成についても、ZrO₂含有量が０．１６ｗｔ％から０．０８ｗｔ％に減少しており、分散させた酸化物の偏析がみられた。
【００６３】
（比較例２）
実施例１と同じ加工物をＴＩＧ溶接により肉盛り接合を行ない、比較例２とした。実施例１と同様に高温クリープ特性を調べ、結果を図１に示した。溶接部の強度は母材強度の４０％であった。分散させた酸化物の偏析がみられた。
【００６４】
（比較例３）
実施例１と同じ加工物をＴＩＧ溶接により接合を行ない、さらに溶接部周辺に同素材のバンドを両面から補強鍛接して比較例３とした。実施例１と同様に高温クリープ特性を調べ、結果を図１に示した。溶接部の強度は母材強度の７０％であった。分散させた酸化物の偏析がみられた。
【００６５】
（比較例４）
予熱工程を設けないこと以外は実施例１と同様に接合を行ない、比較例４とした。可塑性領域の形成の際には摩擦熱により、接合部温度は１３００〜１４００℃に達した。この接合部分の接合強度を調べるために高温クリープ特性を調べ、結果を図１に示した。母材強度に対して１５％の強度が得られた。吸着ガス分子及び結合領域表面に形成された化合物層が可塑性領域全体に分散し、この影響で実施例１よりも強度が低下した。また、図６に接合部分の断面構造の金属組織を示す概念図を示した。接合部内の組成については、酸化物の濃度が０.１５ｗｔ％であり、母材の酸化物の濃度である０.１６ｗｔ％とそれ程差異はなく、結晶サイズにおいても非常に細かいが、ボイドが多量に存在している。
【００６６】
（比較例５）
予熱工程における加熱温度を４５０℃、１５分間加熱保持した以外は実施例２と同様の条件で接合を行なった。可塑性領域の形成の際にプローブピンの摩擦熱により、接合部温度は１３００〜１４００℃に達した。この接合部分の接合強度を調べるために高温クリープ特性を調べ、結果を図１に示した。比較例４とほとんど同じ強度であり、母材強度に対して２０％の強度が得られた。また、接合部分の断面構造の金属組織は比較例４とほとんど同じであり、分散させた酸化物の偏析が見られた。
【００６７】
（比較例６）
予熱工程における加熱温度として融点を若干超える温度とした。このとき接合領域は融着により接合され、これを比較例6とした。したがって、その後の工程である可塑性領域を発生させる工程は行なわなかった。この接合部分の接合強度を調べるために高温クリープ特性を調べ、結果を図１に示した。母材強度に対して３０％の強度が得られた。また、接合部分の断面構造の金属組織の顕微鏡画像を図７に示した。予熱工程における融着によりTIG溶接の場合と同様の現象が起こり、結合領域で結晶粒子が成長していた。さらに分散させた酸化物の偏析が見られた。したがって、予熱工程で融点以上に加熱して融着させてしまうと、TIG溶接と同様に充分な接合強度が得られないことがわかった。
【００６８】
摩擦撹拌接合は、溶接と比較して低い温度で接合可能であることから、接合部における組織の緻密化・組成の安定性・高い強度が得られた。白金合金において、溶接の場合は融点以上の温度となるため１８００℃以上になるが、摩擦撹拌接合の場合は１２００〜１５００℃で接合可能であった。被接合材には予熱が必要であり、且つ、被接合体の裏側に放熱防止用の断熱材を当てることによって、例えば、白金合金を接合する場合は、１２００〜１５００℃の接合温度にすることが可能であった。
【００６９】
本発明の方法を用いてクラック箇所の修理を行なうこともできた。
【００７０】
【発明の効果】
本来、白金族金属又は白金属基合金の接合は、主にＴＩＧ溶接機やガスバーナーを用いて溶接していたが、本発明では摩擦攪拌接合法を白金又は白金基合金の接合に適用する際に金属表面に吸着した吸着ガス分子を除去する目的で予熱工程を設けること或いはその吸着分子と白金との化合物からなる表面に形成された化合物層を除去する目的で予熱工程を意図的に設けることで、接合部における組織の緻密化や組成の安定性、接合部の高い強度を得ることができた。これは、製品の大幅な寿命延長やコストダウンが期待できる。すなわち、強度低下させずに肉盛りやバンドの必要性がなくなった。
【００７１】
また本発明により、白金又は白金基合金からなる加工物とパラジウム、銅、銀若しくはステンレス或いはこれらの金属基合金からなる加工物とを接合する場合に際して、同様に接合部の強度低下を防止することができた。
【００７２】
本発明では予熱工程を大気雰囲気下で行なうことが可能であり、接合作業の容易化、さらには現場での接合作業を可能とした。
【００７３】
さらに本発明では、酸化物分散強化型の白金又は白金基合金を強度低下させることなく接合させることができた。ここで、接合部において金属粒子の粗大化が抑制され且つ強化のために分散させた酸化物粒子の偏析が抑制された接合構造を提供することができた。
【図面の簡単な説明】
【図１】酸化ジルコニウム（ZrO₂）を0.16wt%含有した酸化物分散強化型白金の高温クリープ特性を示す図である。
【図２】実施例１における接合部分の断面構造の金属組織を示す顕微鏡画像である。
【図３】実施例１における接合部分のプローブピンの挿入方向から見た接合後の加工物の表面の顕微鏡画像である。
【図４】実施例１における接合部分のプローブピンの挿入方向の反対方向から見た接合後の加工物の裏面の顕微鏡画像である。
【図５】比較例１におけるTIG突合せ溶接の接合部分の断面構造の金属組織を示す概念図を示した。
【図６】比較例４における接合部分の断面構造の金属組織を示す顕微鏡画像である。
【図７】比較例６における接合部分の断面構造の金属組織を示す顕微鏡画像である。
【図８】TIG溶接で肉盛りをした場合おいて、溶接方向を横切る方向にカットした場合の断面形態を示す概念図である。
【図９】TIG溶接後、バンド補強鍛接をした場合おいて、溶接方向を横切る方向にカットした場合の断面形態を示す概念図である。
【図１０】摩擦攪拌接合法の機構の一形態を示す概念図である。
【符号の説明】
1A,1B,加工物
2,結合領域
3,プローブピン
4,ペンシル部分
7,モータ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a friction stir welding method for joining platinum or a platinum-based alloy and a joining structure thereof, and platinum used for a melting apparatus, a crucible for growing an oxide single crystal, a beat dish for fluorescent X-ray analysis, various pipes, and the like. The present invention can be applied to bonding of platinum or platinum-based alloys.
[0002]
[Prior art]
Conventionally, most products for welding between platinum-based alloys are welded using a TIG (tungsten inert gas) welding machine or a gas burner. Here, TIG welding uses a non-consumable tungsten electrode that generates only an arc between the welding base metal in the atmospheric cutoff gas flowing from the torch, and the weld metal feeds the filler metal from the side of the arc. This is a method of melting and forming. This weld is considerably less strong than the base metal. In particular, the oxide-dispersed reinforced platinum used in glass melting crucibles or the like has a very high strength reduction rate. When the strength difference between the base metal and the welded portion is large, stress is concentrated on the welded portion and often breaks from the periphery.
[0003]
In platinum alloy products used for glass melting devices, oxide single crystal growth crucibles, fluorescent X-ray analysis beat dishes, etc., most products have welded sites. Welding is performed mainly using a TIG welder. However, platinum alloys, especially zirconium oxide (ZrO ₂ ), Calcium oxide (CaO), yttrium oxide (Y ₂ O _Three ) And other oxide-dispersed reinforced platinum welds have weak strength, so there were many troubles around the weld.
[0004]
Therefore, conventionally, as shown in FIG. 8, the strength is prevented from being lowered by building up the welded portion or reinforcing and forging a band of the same material around the welded portion as shown in FIG. 9. Here, the thickness of the platinum alloy product is 0.5 to 5 mm, and the thickness of the reinforcing band is 0.2 to 0.5 mm.
[0005]
Features of TIG welding and welding with a gas burner include relatively easy work and the ability to purchase a welder at a relatively low cost. Overlay welding and band reinforcement forging are necessary because they are largely attributable to prolonging the life of the product even if only a slight increase in strength is obtained.
[0006]
On the other hand, as a metal joining method, for example, Japanese Patent Publication No. 7-505090 and Japanese Patent Publication No. 9-508073 disclose a technique of friction stir welding. Friction Stir Welding is a welding method that enables welding of metals such as iron and aluminum alloys as well as dissimilar metals.
[0007]
As for friction stir welding, there are many investigations on aluminum and aluminum alloys having a relatively low melting point, but there is no report on applying friction stir welding using platinum or a platinum-based alloy as a work piece.
[0008]
[Problems to be solved by the invention]
The friction stir welding method has a lot of knowledge when aluminum alloys and the like are targeted, but no knowledge corresponding to noble metals such as platinum or platinum-based alloys or knowledge corresponding to high melting point materials is found. When the friction stir welding method is adopted for the joining of platinum or a platinum-based alloy, there is no need for build-up or bands, but on the other hand, special attention must be paid to the problem of strength reduction.
[0009]
Usually, a metal adsorbs gas on its surface, and the gas component often causes a chemical reaction such as an oxidation reaction with the metal to form a compound layer on the surface. In the case of friction stir welding, even if the adsorbed gas molecules and the compound layer are present in the joining region, the probe pin inserted into the joining region stirs the plastic region formed by frictional heat. The compound layer is dispersed. Therefore, a larger bonding strength can be obtained as compared with the case where the adsorbed gas molecules and the compound layer are concentrated on the contact surface of the workpiece.
[0010]
However, in the processing of platinum or a platinum-based alloy, a decrease in the strength of the joining portion is a particular problem, so that sufficient bonding strength cannot be obtained even if the adsorbed gas molecules and the compound layer are dispersed throughout the plastic region.
[0011]
Therefore, the present inventor provides a preheating step for the purpose of removing adsorbed gas molecules adsorbed on the metal surface when the friction stir welding method is applied to the bonding of platinum or a platinum-based alloy, or a compound of the adsorbed molecules and platinum. The present invention was completed by finding that a decrease in strength can be suppressed without forming or banding by intentionally providing a preheating step for the purpose of removing the compound layer formed on the surface comprising .
[0012]
That is, the object of the present invention is to provide a preheating step for removing a compound layer such as oxygen formed on the surface of the bonding region when the workpieces made of platinum or a platinum-based alloy are bonded to each other using the friction stir welding method. By providing it, it is possible to eliminate the inclusion of a foreign phase that can be a starting point of breakage, and to prevent the strength of the joint from being lowered. Here, it aims also at prescribing | regulating the optimal heating temperature of the joint area | region in a preheating process.
[0013]
Another object of the present invention is to use a friction stir welding method for bonding a workpiece made of platinum or a platinum-base alloy and a workpiece made of palladium, copper, silver, stainless steel or a metal-base alloy thereof. By providing a preheating step for removing adsorbed gas molecules adsorbed on the surface of the region, it is possible to eliminate the inclusion of voids and voids that can be the starting point of breakage, and to prevent the strength of the joint from being lowered. Joining of dissimilar metals such as palladium, copper, silver, and stainless steel and platinum or a platinum-based alloy, for example, makes the joining of the current heating electrode and platinum strong and leads to stable operation of a furnace or the like.
[0014]
An object of the present invention is to facilitate the joining work by performing the preheating step in an air atmosphere, and further to enable the joining work in the field.
[0015]
Another object of the present invention is to propose an optimal heating method in the preheating process in which the bonding region is irradiated with laser.
[0016]
Furthermore, in the present invention, in order to join platinum or a platinum-based alloy, which is a high melting point material, frictional heat must be effectively concentrated in the joining region. Then, it aims at proposing the heat insulation method for heat dissipation prevention as the means.
[0017]
Further, in the present invention, since it is necessary to heat the joining region to a high temperature by frictional heat, the probe pin is required to have a strength capable of withstanding the high temperature and not to be reactive with platinum. Therefore, an object is to propose an optimal probe pin material to be used.
[0018]
Among platinum and platinum-based alloys, oxide dispersion-strengthened platinum or platinum-based alloys have a severe drop in strength when the dispersed oxide is segregated. Therefore, the present invention proposes a method of joining oxide dispersion strengthened platinum or a platinum-based alloy without reducing the strength.
[0019]
An object of the present invention is to provide a joining structure that cannot be obtained by a conventional joining method in joining oxide dispersion strengthened platinum or a platinum-based alloy. That is, the present invention provides a joint structure in which the coarsening of metal particles is suppressed at the joint and segregation of oxide particles dispersed for strengthening is suppressed.
[0020]
As described above, the present invention changes the joining method from the conventional welding method to the friction stir welding method having a preheating step, thereby greatly improving the strength of the joint portion and extending the life and cost of the conventional product. Is.
[0021]
Another object of the present invention is to apply not only to bonding of platinum or platinum-based alloys but also to repairing cracks.
[0022]
[Means for Solving the Problems]
The friction stir welding method for platinum or platinum-based alloy according to the present invention includes a step of defining the elongated bonding region by bringing the workpieces into contact with each other or substantially contacting each other, and a probe made of a material harder than the material of the workpiece A step of generating frictional heat between the probe pin and the coupling region by rotating the pin into the coupling region and generating a plastic region in the heated coupling region; and solidifying the plastic region to form the workpiece In a friction stir welding method including a step of joining together, the workpiece is made of platinum or a platinum-based alloy, and is adsorbed on the surface of the bonding region in advance before entering the step of generating the plastic region. Adsorbed gas molecules such as oxygen molecules, nitrogen molecules or water molecules Above dissociation temperature And formed on the surface of the binding region Platinum or a platinum-based alloy and the adsorbed gas molecule Providing a preheating step of removing the adsorbed gas molecules and the compound layer by reducing and activating the binding region by heating the binding region to a temperature higher than the dissociation temperature of the compound layer and lower than the melting point of the workpiece. Features.
[0023]
In the friction stir welding method for platinum or platinum-based alloy according to the present invention, it is preferable that in the preheating step, the bonding region is heated to 530 to 1600 ° C. to reduce and activate platinum or the platinum-based alloy.
[0024]
The friction stir welding method for platinum or platinum-based alloy according to the present invention includes a step of defining the elongated bonding region by bringing the workpieces into contact with each other or substantially contacting each other, and a probe made of a material harder than the material of the workpiece A step of generating frictional heat between the probe pin and the coupling region by rotating the pin into the coupling region and generating a plastic region in the heated coupling region; and solidifying the plastic region to form the workpiece In the friction stir welding method comprising a step of joining together,
The workpiece is a combination of a workpiece made of platinum or a platinum-based alloy and a workpiece made of palladium, copper, silver or stainless steel or a metal-based alloy thereof, and before entering the step of generating the plastic region, A preheating step of removing the adsorbed gas molecules by heating the bonded region to a temperature equal to or higher than the dissociation temperature of adsorbed gas molecules such as oxygen molecules, nitrogen molecules or water molecules adsorbed on the surface of the bonded regions and lower than the melting point of the workpiece. It is characterized by providing.
[0025]
In the friction stir welding method for platinum or platinum-based alloy according to the present invention, it is preferable that the preheating step is performed in an air atmosphere.
[0026]
In the friction stir welding method for platinum or platinum-based alloy according to the present invention, it is preferable that in the preheating step, the bonding region is irradiated with a laser and heated.
[0027]
In the friction stir welding method for platinum or platinum-based alloy according to the present invention, it is preferable that a heat insulating material for preventing heat radiation is applied to the coupling region from a direction opposite to the insertion direction of the probe pin.
[0028]
Further, in the friction stir welding method of platinum or platinum-based alloy according to the present invention, a probe pin formed of iridium, rhodium or an alloy thereof is used or aluminum nitride, tantalum nitride, boron nitride having thermal shock resistance is used. Nitride compounds such as titanium nitride, zirconium nitride or hafnium nitride, or carbide compounds such as titanium carbide, zirconium carbide, tantalum carbide, tungsten carbide, boron carbide or hafnium carbide, or hafnium oxide, zirconium oxide or chromium oxide. It is preferable to use a probe pin formed of a material mainly composed of a high melting point oxide or a mixed sintered body thereof.
[0029]
Further, in the friction stir welding method of platinum or platinum-based alloy according to the present invention, the probe pin base is formed of a high melting point metal of 1500 ° C. or higher, and a high hardness ceramic such as titanium nitride is coated on the surface of the base. It is preferable to use a probe pin.
[0030]
Furthermore, in the friction stir welding method for platinum or platinum-base alloy according to the present invention, the platinum or platinum-base alloy is preferably oxide dispersion strengthened platinum or platinum-base alloy.
[0031]
The joined structure of a workpiece made of oxide dispersion-strengthened platinum or a platinum-based alloy joined by the friction stir welding method according to the present invention is a metal particle in a solidified portion of a plastic region. Or platinum-based alloy particles The structure is characterized in that the coarsening of the oxide particles is suppressed and segregation of oxide particles dispersed for strengthening is suppressed.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to embodiments and examples, but the present invention is not construed as being limited to these descriptions.
[0033]
First, the process of the friction stir welding method will be described with reference to FIG. In the friction stir welding method, the work pieces 1A and 1B are brought into contact with each other or are substantially brought into contact with each other to define the elongated coupling region 2, and the probe pin 3 made of a material harder than the material of the work pieces 1A and 1B is rotated. And inserting into the coupling region 2 to generate frictional heat between the probe pin 3 and the coupling region 2 to generate a plastic region in the heated coupling region, and removing the probe pin 3 to solidify the plastic region And a step of joining the workpieces. The probe pin 3 is rotated by a motor 7.
[0034]
Here, the probe pin 3 includes a pencil portion 4. Since the friction between the probe pin 3 and the workpieces 1A and 1B must be performed, the workpieces 1A and 1B must be in contact with each other. The workpiece may be substantially in contact with the friction. Further, in order to perform continuous joining instead of spot joining, the joining region 2 must be elongated, and if there is a large space in the joining region, friction between the probe pin 3 and the workpieces 1A and 1B is not performed. Furthermore, the probe pin must withstand frictional heat and have a strength that can withstand torsional stress due to rotation.
[0035]
Next, the principle of the friction stir welding method will be described. The workpieces 1A and 1B are butted together, the probe pin 3 is rotated, and the pencil portion 4 is slowly pushed into the butting line which is the coupling region 2. The length of this pencil part 4 shall be required for the welding depth. As the probe pin 3 rotates and contacts the coupling area 2, friction causes the material at the point of contact to rapidly heat, resulting in a decrease in the mechanical strength of the material. When further force is applied, the probe pin 3 kneads and pushes the material along its movement 8. In the joining area 2, the frictional heat generated by the rotating cylindrical shoulder of the probe pin 3 and the pencil part 4 creates a high temperature plastic area under the shoulder and in the metal around the pencil part. When the workpiece moves in the opposite direction to the movement of the probe pin 3 or vice versa, the plasticized metal is crushed at the front end of the probe pin 3 in the traveling direction, and mechanical forging and forging according to the shape and rotation direction of the probe pin 3 are performed. It moves to the rear end by the action. As a result, the joint on the front of the instrument is heated, creating a plastic region. The plastic region is cooled at the rear end of the tool while stirring the crushed metal that breaks the oxide film present on the workpiece, and forms a solid weld. All this phenomenon occurs at a temperature lower than the melting point of the work piece.
[0036]
Friction stir welding eliminates the generation of cracks, there is no loss of alloy elements due to evaporation of the weld metal, the alloy components can be held as they are, and a fine granular structure is formed on the weld metal by press-fitting, stirring and forging actions of the welding tool. There is a merit that
[0037]
Next, the friction stir welding method for platinum or platinum-based alloy of the present invention will be described. In the first embodiment of the present invention, the workpieces 1A and 1B are workpieces made of platinum or a platinum-based alloy. Then, before entering the step of generating the plastic region, the adsorbed gas molecules such as oxygen molecules, nitrogen molecules or water molecules adsorbed on the surface of the binding region and the dissociation of the compound layer such as oxygen formed on the surface of the binding region in advance. A preheating step of removing the adsorbed gas molecules and the compound layer by reducing and activating the bonding region by heating the bonding region above the temperature and below the melting point of the workpiece is provided.
[0038]
Here, the platinum-based alloy is a multi-component alloy containing 50 wt% or more of platinum, for example, a platinum-zirconium alloy, a platinum-yttrium alloy, a platinum-rhodium alloy, a platinum-iridium alloy, a platinum-zirconium-rhodium alloy, There are platinum-zirconium-gold alloys and the like. Oxide dispersion strengthened platinum is a kind of platinum-based alloy.
[0039]
Usually, oxygen molecules, nitrogen molecules, and water molecules in the air are adsorbed on the surface of platinum or a platinum-based alloy. Here, in many cases, a compound layer such as an oxide layer (PtO) is formed on the surface by water molecules. In normal friction stir welding, the plastic region formed by frictional heat is agitated by the probe pin, so that the adsorbed gas molecules and the oxide layer are mixed and dispersed in the plastic region. Even when platinum or a platinum-based alloy is used as a workpiece, the adsorbed gas molecules and the compound layer are similarly dispersed and mixed in the plastic region.
[0040]
In the present invention, platinum or platinum-based alloy workpieces are often used at high temperatures such as glass melting crucibles. Under such severe conditions of use, stress concentrates on the adsorbed gas molecules and the compound layer dispersed and mixed in the plastic region, which becomes the starting point of fracture of the joint portion. Therefore, in the present invention, before entering the step of generating the plastic region, a preheating step for removing the adsorbed gas molecules and the compound layer in advance is provided. The preheating condition is to heat the bonding region to a temperature higher than the dissociation temperature of the adsorbed gas molecules and the compound layer on the surface of the bonding region and lower than the melting point of the workpiece. By heating to the above temperature, the adsorbed gas molecules adsorbed on the surface of the binding region can be completely dissociated, and further, the surface can be reduced and activated to dissociate the compound layer.
[0041]
If the heating in the preheating step is lower than the dissociation temperature, voids remain or impurities due to the compound layer remain. Therefore, in the case of platinum or a platinum-based alloy, when the temperature is set to 530 ° C. or higher, it is possible to eliminate the oxidized layer formed on the surface by being reduced and activated even in an oxygen-containing atmosphere. In the present invention, the temperature is preferably set to 600 ° C. or higher in order to increase the reduction activity. On the other hand, the melting point of platinum is approximately 1770 ° C., and if it exceeds the melting point, it will be liquefied, so that it will be fused in the joining region, or the workpiece will not be able to maintain its shape by melting. Therefore, it is preferable to perform the preheating step at 1600 ° C. or lower in order to set the heating upper limit temperature to the melting point or lower and form a plastic region after the preheating step and stir. Therefore, in the preheating step, it is preferable to heat to 530 ° C. or higher and lower than 1600 ° C., more preferably 600 ° C. to 1500 ° C. Here, by heating to 600 ° C. or higher and 1500 ° C. or lower, platinum or a platinum-based alloy can be recrystallized in the preheating step. By recrystallization, the crystal particles are softened, and the stirring efficiency can be increased when the plastic region is formed in the next step.
[0042]
In the preheating step, heating is performed for a predetermined time in order to desorb the adsorbed gas molecules on the surface of the binding region and to completely remove the compound layer. Although the necessary heating and holding time differs depending on the heating temperature, for example, when heating to 600 ° C., it is preferable to hold for 5 to 10 minutes. If it is less than 5 minutes, the separation of adsorbed gas molecules and the removal of the compound layer will be insufficient, and internal defects will also occur. Further, if it is 10 minutes or longer, the working efficiency becomes unfavorable. Note that when the heating temperature is high, the reduction activity can be increased, so that the separation of the adsorbed gas molecules and the removal of the compound layer proceed, and the heat holding time can be shortened.
[0043]
If the heating and holding time is longer than necessary, the recrystallized particles grow secondary and cause coarsening of the particles. After the preheating step, the plastic region is agitated by the probe pin, but if the recrystallized particles that have become coarse due to insufficient agitation remain, the strength will decrease, so the heating and holding time will be sufficient to prevent coarsening of the recrystallized particles. To do.
[0044]
In the second embodiment of the present invention, a combination of a workpiece made of platinum or a platinum-based alloy and a workpiece made of palladium, copper, silver, stainless steel, or a metal-based alloy thereof is joined. Then, before entering the step of generating the plastic region, the bonding is performed at a temperature higher than the dissociation temperature of adsorbed gas molecules such as oxygen molecules, nitrogen molecules or water molecules adsorbed on the surface of the bonding region of the workpiece and lower than the melting point of the workpiece. A preheating step is provided in which the region is heated to remove adsorbed gas molecules adsorbed on the surface of the binding region.
[0045]
As described in the first embodiment, adsorption gas molecules such as oxygen molecules, nitrogen molecules or water molecules are adsorbed on the surface of platinum or a platinum-based alloy, and palladium, copper, silver or stainless steel which is a different metal from platinum. Alternatively, similar adsorbed gas molecules exist on the surface of these metal-based alloys. In the present invention, a preheating step is provided in the joint portion in order to prevent a decrease in strength due to the influence of the adsorbed gas molecules.
[0046]
Preheating conditions are such that the temperature is higher than the dissociation temperature of the adsorbed gas molecules and lower than the melting point of the workpiece. There are two types of adsorption: chemical adsorption and physical adsorption. The case where the adsorbed component has a strong chemical bond with the solid surface is called chemical adsorption, and examples include adsorption of oxygen and hydrogen on a metal. This can be considered as a chemical reaction between the metal and the gas on the surface, and the heat generated during the adsorption is large, and the gas does not easily leave the metal. In contrast, physical adsorption between the molecule of the component to be adsorbed and the solid surface, that is, the case where adsorption occurs due to van der Waals force, etc. is called physical adsorption, and the heat generated during adsorption in this case is , Slightly higher than the heat of condensation of the adsorbed molecules. In the present invention, it is necessary to remove oxygen and water chemically adsorbed on the metal surface. Although the dissociation temperature differs depending on the metal species, the present invention heats to 400 ° C. or higher. If the heating in the preheating step is lower than the dissociation temperature, voids remain or impurities due to the compound layer remain.
[0047]
Here, if heated to 530 ° C. or higher as in the first embodiment, the surface of the bonded region of the workpiece made of platinum or a white metal alloy is reduced and activated even in an oxygen-containing atmosphere and formed on the surface. It is possible to eliminate the oxidized layer, and if the temperature is 600 ° C. or higher, the reduction activity can be enhanced. Therefore, in 2nd Embodiment, the heating minimum temperature in a preheating process shall be 400 degreeC, Preferably it is 530 degreeC, More preferably, you may be 600 degreeC. By heating to 600 ° C. or higher, the workpiece can be recrystallized in the preheating step. By recrystallization, the crystal particles are softened, and the stirring efficiency can be increased when the plastic region is formed in the next step.
[0048]
On the other hand, setting the heating upper limit temperature below the melting point is for preventing fusion or maintaining the shape of the workpiece as described above. For the melting point of the workpiece, a temperature with a low melting point is selected from the combined workpieces in order to prevent melting of the workpiece. Usually, since the melting point of platinum or a platinum-based alloy is high, the upper limit of heating temperature is set to be less than the melting point of a dissimilar metal. The melting point of palladium is 1554 ° C., the melting point of copper is 1083 ° C., the melting point of silver is 961 ° C., and the melting point of stainless steel varies depending on the type, for example, 1510 ° C. for martensitic stainless steel. However, since it liquefies when the melting point is exceeded, the heating upper limit temperature is preferably set as follows in order to form a plastic region and stir after the preheating step. When the dissimilar metal is palladium, it is 1300 ° C. or less, when copper is 800 ° C. or less, when silver is 700 ° C. or less, and when stainless is martensitic stainless steel, it is 1250 ° C. or less.
[0049]
Also in the second embodiment, heating is performed for a predetermined time in order to desorb the adsorbed gas molecules on the surface of the binding region in the preheating step. Although the necessary heating and holding time differs depending on the heating temperature, for example, when heating to 600 ° C., it is preferable to hold for 5 to 10 minutes. If it is less than 5 minutes, the adsorbed gas molecules will be insufficiently detached, and internal defects will also occur. Further, if it is 10 minutes or longer, the working efficiency becomes unfavorable. However, as in the first embodiment, the heating and holding time is set to a time that does not cause coarsening of the recrystallized particles.
[0050]
In the first and second embodiments, in the present invention, the compound layer formed on the surface of the binding region is removed by utilizing reduction activation of platinum or a platinum-based alloy at 530 ° C. or higher. Chemicalization also works under atmospheric conditions. Therefore, in the present invention, special atmosphere adjustment is unnecessary, and there is an advantage that the joining work can be performed on site.
[0051]
In the preheating process, heating in the bonding area of the work piece is performed by energization heating, heating around the bonding area with a platinum heater, local heating around the bonding area using a gas burner, plasma torch, etc. In addition, it is preferable to heat the surface by irradiating with a laser so as not to affect the surface other than heating. In this case, YAG laser, CO ₂ It is a laser.
[0052]
In addition, by applying a heat insulating material to the bonding area from the opposite direction to the probe pin insertion direction during heating in the preheating process, the temperature distribution in the bonding area is corrected and the adsorbed gas molecules are dissociated. The reduction activation is preferably performed without unevenness. As the heat insulating material, ceramics having a small thermal conductivity such as alumina is preferable.
[0053]
The selection criteria for the probe material are that it is harder than the bonding material, has excellent wear resistance, does not crack or chip during processing, does not wear or deteriorate due to oxidation, and does not easily form an alloy with the bonding material. And so on. Therefore, for ceramics such as aluminum oxide and zirconium oxide, there is a problem of cracking and chipping during processing, and for refractory metals such as tungsten, tantalum, niobium, molybdenum, ruthenium, there is consumption and deterioration due to oxidation, Not suitable for probe material. Therefore, in the present invention, a probe pin formed of iridium, rhodium or an alloy thereof is used. Iridium has a melting point of 2457 ° C. and rhodium has a melting point of 1963 ° C., which is a higher melting point material than platinum. Examples of the alloy include an iridium base alloy, a rhodium base alloy, and an iridium-rhodium alloy.
[0054]
Further, the probe pin may be formed of a material having a thermal shock resistance, a nitride compound, a carbide compound, a high melting point oxide, or a mixed sintered body thereof as a main component. Examples of nitride compounds include aluminum nitride, tantalum nitride, boron nitride, titanium nitride, zirconium nitride, and hafnium. Examples of carbide compounds include titanium carbide, zirconium carbide, tantalum carbide, tungsten carbide, boron carbide, and carbonized carbide. Hafnium can be exemplified, and examples of the high melting point oxide include hafnium oxide, zirconium oxide, and chromium oxide. All of these have a higher melting point and higher thermal shock resistance than platinum.
[0055]
Further, as the probe pin, a probe pin base may be formed of a high melting point metal having a temperature of 1500 ° C. or higher, and a high hardness ceramic such as titanium nitride may be coated on the surface of the base. Examples of the refractory metal include tungsten, tantalum, molybdenum, iridium and the like.
[0056]
In the present invention, by adhering to the heating temperature and heating time as described above in the preheating step, the adsorbed gas molecules and the compound layer on the surface of the binding region are removed, and the bonding is performed while preventing the recrystallized particles from becoming coarse. Therefore, the bonded structure of the workpiece made of oxide dispersion-strengthened platinum or a platinum-based alloy is obtained by suppressing the coarsening of the metal particles in the solidified portion of the plastic region and of the oxide particles dispersed for strengthening. A structure in which segregation is suppressed is obtained. The joint structure welded using a TIG welder or gas burner has a structure in which the crystal grains of platinum are coarsened and oxide particles dispersed for strengthening at the grain boundaries are segregated. Then, the strength is extremely lowered. On the other hand, the joint structure of the present invention realizes prevention of particle coarsening and prevention of segregation of oxide particles, and prevents strength reduction at the joint.
[0057]
The thickness of the workpiece is 1 to 3 mm, the shaft diameter of the probe pin is 8 to 12 mm, the diameter of the pencil portion of the probe pin is 1 to 3 mm, and the length of the pencil portion of the probe pin depends on the thickness of the workpiece. For example, about 0.7 to 2.7 mm, the rotation speed of the probe pin is 500 to 1500 rpm, and the movement speed of the probe pin is 20 to 50 mm / s. Further, in order to create a plastic region, the heating by the frictional heat of the probe pin is 1200 to 1500 ° C. in the case of bonding between platinum or platinum-based alloys, and 500 to 500 in the case of bonding between dissimilar metals and platinum or platinum-based alloys. The temperature is 1400 ° C., and when different workpieces are joined, the temperature is lower than the lower melting point.
[0058]
【Example】
Examples are shown below.
(Example 1)
Workpiece material is ZrO ₂ Was added in an oxide dispersion type reinforced platinum to which 0.16 wt% was added, and the same kind of workpiece was joined in the air atmosphere. The processed product was a plate material, and the thickness of the plate material was 2 mm. The material of the probe pin was iridium. The probe pin shaft diameter was 10 mm, the probe pin diameter was 1.5 mm, and the pencil part length was 1.7 mm. The side of the workpiece was abutted to define the coupling region, and alumina was applied to the coupling region from the opposite direction to the probe pin insertion direction as a heat insulating material for preventing heat dissipation. Next, the periphery of the bonding region was heated by a platinum heater that entered the preheating step. The heating temperature was 600 ° C., and the heating was held for 10 minutes. After the preheating step, the next step is to form a plastic region. The probe pin was rotated at a rotation speed of 800 rpm and inserted into the bonding area. After the plastic region was formed, the probe pin was moved along the line of the binding region. The moving speed at this time was 30 mm / s. The joint temperature reached 1300 to 1400 ° C. due to frictional heat. The plastic area that was scanned with the probe pin solidified with natural cooling. After scanning the entire binding area with the probe pin, the probe pin was pulled out of the workpiece while rotating. Thereby, two workpieces were joined. In order to investigate the joint strength of this joint part, the high temperature creep characteristics were measured using a high temperature creep furnace (made in-house). The results are shown in FIG. Note that the measurement was performed in an air atmosphere at 1500 ° C. A strength of 90% or more with respect to the base material strength was obtained. Moreover, the microscope image which shows the metal structure of the cross-section of a junction part in FIG. 2 was shown. Here, the structure of the cross section of the workpiece is a base material structure, and the central portion is a structure of a welded portion (hereinafter, the same in a microscopic image showing a metal structure of a cross-sectional structure). Although the crystal size was larger than that of the base material, it was very fine and growth of crystal grains was suppressed. In addition, undulation is generated in the crystal itself. Regarding the composition in the joint portion, the oxide concentration was 0.15 wt%, which was not so different from the base oxide concentration of 0.16 wt%, and no segregation of the dispersed oxide was observed. Furthermore, the microscope image of the surface of the workpiece after joining seen from the insertion direction of the probe pin is shown in FIG. 3, and the microscope image of the back surface of the workpiece is shown in FIG.
[0059]
(Example 2)
Bonding was performed in the same manner as in Example 1 except that a laser (Daihen, APELIO 2510V) was used as a heating method in the preheating step. The same results as in Example 1 were obtained, and it was confirmed that bonding could be performed without reducing the strength.
[0060]
(Example 3)
Bonding was performed under the same conditions as in Example 2 except that the heating temperature in the preheating step was 1200 ° C. and maintained for 5 minutes. The joint temperature reached 1300 to 1400 ° C. due to the frictional heat of the probe pin during the formation of the plastic region. Similar to Example 1, a strength of 90% or more with respect to the base material strength was obtained. Further, the metal structure of the cross-sectional structure of the joint portion was similar to that in FIG. 2, the crystal size was very fine, the growth of crystal grains was suppressed, and the crystal itself was swelled. Regarding the composition in the joint portion, the oxide concentration was 0.15 wt%, which was not so different from the base oxide concentration of 0.16 wt%, and no segregation of the dispersed oxide was observed.
[0061]
(Example 4)
One side of the workpiece material is ZrO ₂ The oxide dispersion type reinforced platinum added with 0.16 wt% was used as the other, and the other workpieces were joined in an air atmosphere. Both processed materials were plate materials, and the thickness of the plate materials was 2 mm. The material of the probe pin was iridium. The other conditions were the same as in Example 1. Due to the frictional heat, the joint temperature reached 1300-1400 ° C., the plastic region solidified and the two workpieces were joined. The bonding strength was 2.0 times that of the case where these workpieces were bonded by TIG.
[0062]
(Comparative Example 1)
The same workpiece as Example 1 was butt-joined by TIG welding to obtain Comparative Example 1. The high temperature creep characteristics were examined in the same manner as in Example 1, and the results are shown in FIG. The strength of the welded portion was 30 to 40% of the base material strength. Moreover, the conceptual diagram which shows the metal structure of the cross-section of a junction part in FIG. 5 was shown. As shown in FIG. 5, the TIG welded product had a large crystal size and crystal grains grew. The composition in the joint is also ZrO ₂ The content decreased from 0.16 wt% to 0.08 wt%, and segregation of the dispersed oxide was observed.
[0063]
(Comparative Example 2)
The same workpiece as Example 1 was subjected to build-up joining by TIG welding to obtain Comparative Example 2. The high temperature creep characteristics were examined in the same manner as in Example 1, and the results are shown in FIG. The strength of the welded portion was 40% of the base material strength. Segregation of the dispersed oxide was observed.
[0064]
(Comparative Example 3)
The same workpiece as in Example 1 was joined by TIG welding, and a band of the same material was reinforced and welded from both sides around the welded portion to obtain Comparative Example 3. The high temperature creep characteristics were examined in the same manner as in Example 1, and the results are shown in FIG. The strength of the weld was 70% of the base metal strength. Segregation of the dispersed oxide was observed.
[0065]
(Comparative Example 4)
Joining was performed in the same manner as in Example 1 except that the preheating process was not provided, and Comparative Example 4 was obtained. During the formation of the plastic region, the joint temperature reached 1300 to 1400 ° C. due to frictional heat. In order to investigate the joint strength of this joint part, the high temperature creep characteristics were examined, and the results are shown in FIG. A strength of 15% with respect to the base material strength was obtained. The compound layer formed on the surface of the adsorbed gas molecules and the binding region was dispersed throughout the plastic region, and the strength was lower than that of Example 1 due to this influence. Moreover, the conceptual diagram which shows the metal structure of the cross-section of a junction part in FIG. 6 was shown. As for the composition in the joint, the oxide concentration is 0.15 wt%, which is not so different from the base oxide concentration of 0.16 wt%, and the crystal size is very fine, but there are many voids. Exists.
[0066]
(Comparative Example 5)
Joining was performed under the same conditions as in Example 2 except that the heating temperature in the preheating step was 450 ° C. for 15 minutes. The joint temperature reached 1300 to 1400 ° C. due to the frictional heat of the probe pin during the formation of the plastic region. In order to investigate the joint strength of this joint part, the high temperature creep characteristics were examined, and the results are shown in FIG. The strength was almost the same as that of Comparative Example 4, and a strength of 20% with respect to the base material strength was obtained. Moreover, the metal structure of the cross-sectional structure of the joint portion was almost the same as in Comparative Example 4, and segregation of the dispersed oxide was observed.
[0067]
(Comparative Example 6)
The heating temperature in the preheating step was set slightly above the melting point. At this time, the joining region was joined by fusion, and this was designated as Comparative Example 6. Therefore, the subsequent step of generating the plastic region was not performed. In order to investigate the joint strength of this joint part, the high temperature creep characteristics were examined, and the results are shown in FIG. A strength of 30% with respect to the base material strength was obtained. Moreover, the microscope image of the metal structure of the cross-sectional structure of a junction part was shown in FIG. The same phenomenon as in the case of TIG welding occurred due to fusion in the preheating process, and crystal grains grew in the bonding region. Further, segregation of the dispersed oxide was observed. Therefore, it has been found that if the preheating step is performed by heating to the melting point or higher, sufficient bonding strength cannot be obtained as in TIG welding.
[0068]
Friction stir welding can be joined at a lower temperature than welding, and therefore, densification of the structure, stability of the composition, and high strength were obtained at the joint. In the case of a platinum alloy, the temperature is equal to or higher than the melting point in the case of welding, so that the temperature is 1800 ° C. or higher. In the case of friction stir welding, bonding was possible at 1200 to 1500 ° C. The material to be joined needs to be preheated, and by applying a heat insulating material for preventing heat dissipation to the back side of the object to be joined, for example, when joining a platinum alloy, the joining temperature should be 1200 to 1500 ° C. Was possible.
[0069]
It was also possible to repair cracks using the method of the present invention.
[0070]
【The invention's effect】
Originally, the joining of platinum group metals or white metal-based alloys was mainly performed using a TIG welding machine or a gas burner. In the present invention, however, the friction stir welding method is applied to the joining of platinum or platinum-based alloys. A preheating step is provided for the purpose of removing adsorbed gas molecules adsorbed on the metal surface, or a preheating step is intentionally provided for the purpose of removing the compound layer formed on the surface composed of the compound of the adsorbed molecules and platinum. Thus, it was possible to obtain a dense structure in the joint, stability of the composition, and high strength of the joint. This can be expected to greatly extend the product life and reduce costs. That is, there was no need for overlay or band without reducing the strength.
[0071]
In addition, according to the present invention, when joining a workpiece made of platinum or a platinum-base alloy and a workpiece made of palladium, copper, silver, stainless steel, or a metal-base alloy thereof, the strength reduction of the joint portion is similarly prevented. I was able to.
[0072]
In the present invention, the preheating step can be performed in an air atmosphere, which facilitates the joining work and further enables the joining work in the field.
[0073]
Furthermore, in the present invention, it was possible to join oxide dispersion strengthened platinum or a platinum-based alloy without reducing the strength. Here, it was possible to provide a joint structure in which the coarsening of the metal particles was suppressed in the joint and segregation of the oxide particles dispersed for strengthening was suppressed.
[Brief description of the drawings]
[Fig.1] Zirconium oxide (ZrO) ₂ Is a diagram showing the high-temperature creep characteristics of oxide dispersion strengthened platinum containing 0.16 wt%).
2 is a microscopic image showing a metal structure of a cross-sectional structure of a joint portion in Example 1. FIG.
FIG. 3 is a microscopic image of the surface of the workpiece after joining as seen from the insertion direction of the probe pin at the joining portion in Example 1.
4 is a microscopic image of a back surface of a workpiece after joining, viewed from the direction opposite to the insertion direction of the probe pin at the joining portion in Example 1. FIG.
5 is a conceptual diagram showing a metal structure of a cross-sectional structure of a joint portion of TIG butt welding in Comparative Example 1. FIG.
6 is a microscopic image showing a metal structure of a cross-sectional structure of a joint portion in Comparative Example 4. FIG.
7 is a microscopic image showing a metal structure of a cross-sectional structure of a joint portion in Comparative Example 6. FIG.
FIG. 8 is a conceptual diagram showing a cross-sectional form when cutting is performed in a direction crossing the welding direction when building up by TIG welding.
FIG. 9 is a conceptual diagram showing a cross-sectional form when cut in a direction crossing the welding direction in the case of performing band reinforcement forging after TIG welding.
FIG. 10 is a conceptual diagram showing an embodiment of a mechanism of a friction stir welding method.
[Explanation of symbols]
1A, 1B, work piece
2, joining area
3, probe pin
4, pencil part
7, motor

Claims

A step of defining the elongated coupling region by bringing the workpieces into contact with each other or substantially contacting each other, and inserting the probe pin made of a material harder than the material of the workpiece into the coupling region while rotating the probe pin and the coupling region In the friction stir welding method comprising the steps of generating frictional heat between and generating a plastic region in the heated bonded region, solidifying the plastic region and bonding the workpieces together,
An adsorbed gas molecule such as an oxygen molecule, a nitrogen molecule or a water molecule adsorbed on the surface of the binding region in advance before entering the step of generating the plastic region, wherein the workpiece is made of platinum or a platinum-based alloy. The bonding region is heated by heating the bonding region to a temperature equal to or higher than the dissociation temperature of the compound layer of platinum or a platinum-based alloy formed on the surface of the bonding region and the adsorbed gas molecule and lower than the melting point of the workpiece. A friction stir welding method for platinum or a platinum-based alloy, characterized in that a preheating step for removing the adsorbed gas molecules and the compound layer by reducing and activating the region is provided.

The platinum or platinum-based alloy friction stir welding method according to claim 1, wherein in the preheating step, the bonding region is heated to 530 to 1600 ° C. to reduce and activate platinum or the platinum-based alloy.

A step of defining the elongated coupling region by bringing the workpieces into contact with each other or substantially contacting each other, and inserting the probe pin made of a material harder than the material of the workpiece into the coupling region while rotating the probe pin and the coupling region In the friction stir welding method comprising the steps of generating frictional heat between and generating a plastic region in the heated bonded region, solidifying the plastic region and bonding the workpieces together,
The workpiece is a combination of a workpiece made of platinum or a platinum-based alloy and a workpiece made of palladium, copper, silver or stainless steel or a metal-based alloy thereof, and before entering the step of generating the plastic region, A preheating step of removing the adsorbed gas molecules by heating the bonded region to a temperature equal to or higher than the dissociation temperature of adsorbed gas molecules such as oxygen molecules, nitrogen molecules or water molecules adsorbed on the surface of the bonded regions and lower than the melting point of the workpiece. A friction stir welding method for platinum or a platinum-based alloy characterized by comprising:

The friction stir welding method for platinum or a platinum-based alloy according to any one of claims 1 to 3 , wherein the preheating step is performed in an air atmosphere.

In the preheating step, the friction stir welding of platinum or platinum based alloy according to any one of claims 1, 2, 3 or 4, characterized in that heating by irradiating laser to the coupling region.

Platinum according to any one of claims 1, 2, 3, 4 or 5, characterized in that shed insulation for heat radiation preventing the binding region from the opposite direction to the insertion direction of the probe pin Or friction stir welding of platinum-based alloys.

Nitride compounds such as aluminum nitride, tantalum nitride, boron nitride, titanium nitride, zirconium nitride or hafnium nitride or titanium carbide, which use probe pins formed of iridium or rhodium or their alloys, or have thermal shock resistance A material mainly composed of a carbide compound such as zirconium carbide, tantalum carbide, tungsten carbide, boron carbide or hafnium carbide, a high melting point oxide such as hafnium oxide, zirconium oxide or chromium oxide, or a mixed sintered body thereof. The formed probe pin is used, The platinum or platinum-base alloy friction stir welding method according to any one of claims 1, 2, 3, 4, 5, or 6.

The probe pin base is formed of a high melting point metal having a temperature of 1500 ° C. or higher, and a probe pin having a surface coated with a high-hardness ceramic such as titanium nitride is used. 4. The friction stir welding method for platinum or platinum-based alloy according to any one of 4, 5, 6 or 7.

The platinum or platinum-based alloy is oxide dispersion strengthened platinum or a platinum-based alloy, according to any one of claims 1, 2, 3, 4, 5, 6, 7, or 8. Friction stir welding method for platinum or platinum-based alloy as described.

The work structure of the oxide dispersion-strengthened platinum or platinum-base alloy welded by the friction stir welding method according to claim 9 is such that the metal particles or platinum-base alloy particles are coarsened in the solidified portion of the plastic region. A bonded structure of platinum or a platinum-based alloy, characterized in that it is a structure that is suppressed and segregation of oxide particles dispersed for strengthening is suppressed.