JP2004076095A

JP2004076095A - Sintered titanium alloy and its manufacturing method

Info

Publication number: JP2004076095A
Application number: JP2002237750A
Authority: JP
Inventors: Kiyotaka Kato; 加藤　清隆; Norihiko Yamada; 山田　敬彦
Original assignee: National Institute of Advanced Industrial Science and Technology AIST
Current assignee: National Institute of Advanced Industrial Science and Technology AIST
Priority date: 2002-08-19
Filing date: 2002-08-19
Publication date: 2004-03-11
Anticipated expiration: 2022-08-19
Also published as: JP3728507B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method to manufacture easily an(α+β) two phase Ti alloy sintered material which exhibits light weight, high strength, and high corrosion resistance by powder metallurgy process, and a product manufactured by the method. <P>SOLUTION: A manufacturing method of a Ti sintered alloy which shows high tensile property consists of process of adding an intermetallic compound of FeAl<SB>3</SB>to a pure Ti powder which contains not more than 0.2 mass% oxygen, and blending to form a blended powder, and then, making the blended powder into a green compact, and forming two phase structure of (α+β) and, a relative density of a sintered compact is made 94% or more by non-pressurized sintering in a vacuum, and by internal reaction. A two phase Ti alloy sintered compact whose relative density is 94% or more is manufactured by the above method. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、焼結チタン合金及びその製造方法に関するものであり、更に詳しくは、軽量、高強度、高耐食性を有し、かつ安価に製造することが可能な相対密度が９４％以上の（α＋β）二相チタン焼結合金及びその製造方法に関するものである。
【０００２】
【従来の技術】
一般に、チタンは、軽量、高耐食性の優れた特性を有することから、例えば、宇宙・航空機器分野、輸送機器分野、化学プラント分野等において、鉄系材料に代わる適用が期待されている。また、生体適合性にも優れていることから、例えば、医療分野及び時計や眼鏡などの身につける装飾品分野への利用も進んでいる。しかしながら、他の元素を含まない純チタンは、α単相組織であり、引張強度や硬度が必ずしも高いとは言えない。従って、高い強度特性を必要とする構造部材として実際に使用されるのは、Ｔｉ−６Ａｌ−４Ｖ合金を初めとする（α＋β）　二相合金である。
【０００３】
これまでは、この様なチタン合金部材の製造には、溶解鋳造法が主に使用されていたが、この方法は、溶解時の１５００℃を越える高温ではチタンは活性が高くなることから、技術的に困難な点が多い。また、チタン合金は、純チタンに比較して硬度が高く、難加工性材料であるため、機械加工による部品製造にも困難が伴う。このチタン合金の活性の高さ及び難加工性を克服するために、近年、粉末冶金法によるチタン合金の成形技術の研究開発が進められている。
【０００４】
この粉末冶金法の利点としては、チタン合金の融点以下の温度で、焼結により部材を製造するため、ハンドリングが容易であること、成形後の後加工の少ないニアネットシェイプ成形が可能であること、及び結晶粒が微細であるため機械的性質が優れること、が挙げられる。粉末冶金法の中には様々なプロセスがあり、例えば、プレス成形、ＣＩＰ成形、押出し成形、粉末射出成形などがあり、いずれの成形法も、目的とする形状に成形した後、焼結の工程を経て目的とする形状部材を得るプロセスからなる。プロセスによっては、成形を容易にするため、粉末にバインダーを添加するが、その場合、焼結の前に脱バインダーを行う。これらの成形法のうち、特に、複雑形状部品を量産する技術として、粉末射出成形法が有力である。
【０００５】
粉末冶金法によりチタン合金焼結体を作製する場合、原料となる粉末に関しては、（１）あらかじめ目的とする成分に合金化された粉末を用いる合金粉末法、（２）純チタン粉末と合金成分となる粉末（単一元素粉末あるいは化合物粉末のいずれか、もしくはその組み合わせ）を混合した素粉末混合法、の２種類の方法がある。これらのうち、上記（１）の合金粉末法は、粉末自体が合金化されているため、均質で安定した組織及び特性の焼結体が得られるが、Ｔｉ合金粉末の製造は、技術的に困難であるため、市販されているものはごく限られた一部の組成のものしかなく、しかも、非常に高価である。特に、粉末射出成形に使用できる様な微細な合金粉末は、ほとんどないといっても過言ではない。従って、粉末冶金法で目的とする組成のチタン合金を作製するためには、上記（２）の素粉末混合法によることがほとんどである。
【０００６】
これまでの代表的な（α＋β）　二相Ｔｉ合金として、Ｔｉ−６Ａｌ−４Ｖ合金がある。この合金を素粉末混合法による焼結法で製造するには、Ｔｉ粉末と６０Ａｌ−４０Ｖ粉末を９：１（重量比）で混合して、成形・焼結することがこれまで行われてきている。しかし、６０Ａｌ−４０Ｖ粉末は、非常に高価な上、Ｖは生体毒性が指摘されており、Ｔｉ合金の有望な用途である生体材料への適用が今後制限されることが考えられる。この様なことから、当該技術分野においては、粉末冶金法によるＴｉ−６Ａｌ−４Ｖに代わる新たな合金の開発が期待されていた。
【０００７】
【発明が解決しようとする課題】
このような状況の中で、本発明者らは、上記従来技術に鑑みて、上記Ｔｉ−６Ａｌ−４Ｖ合金に代わる低コスト性と生体適合性を満たす新しい合金材料を開発することを目標として鋭意研究を積み重ねた結果、ＶをＦｅに置き換えたＴｉ−Ａｌ−Ｆｅ系合金の焼結体を作製することにより所期の目的を達成することを見出し、本発明を完成するに至った。
すなわち、本発明は、粉末冶金法、特に、粉末射出成形法により、軽量、高強度、高耐食性を発揮する（α＋β）　二相Ｔｉ合金焼結材を比較的簡単に製造する方法及びその製品を提供することを目的とするものである。
【０００８】
【課題を解決するための手段】
上記課題を解決するための本発明は、以下の技術的手段から構成される。
（１）酸素量が０．２５ｍａｓｓ％以下の純Ｔｉ粉末に、金属間化合物のＦｅＡｌ_３　粉末を１〜１０ｍａｓｓ％添加、混合して混合粉末を形成した後、これを圧粉体とし、真空中で無加圧焼結して内部反応により（α＋β）の二相組織を生成させ、かつ焼結体の相対密度を９４％以上にすることを特徴とする二相Ｔｉ合金焼結体の製造方法。
（２）酸素量が０．２５ｍａｓｓ％以下の純Ｔｉ粉末に、金属間化合物のＦｅＡｌ_３　粉末を１〜１０ｍａｓｓ％添加、混合して混合粉末を形成した後、この混合粉末を所定の形状に成形し、相対密度が９４％以上になるように所定の温度において真空中で無加圧焼結して（α＋β）の二相Ｔｉ合金焼結体を得ることを特徴とするＴｉ焼結合金の製造方法。
（３）焼結温度が、１０００〜１３００℃である、前記（１）又は（２）に記載の方法。
（４）混合粉末に有機バインダーを３０〜５０ｖｏｌ．％添加して加熱混練し、これを所定の形状に射出形成した後、脱バインダー工程を経て真空中で無加圧焼結する、前記（２）に記載の方法。
（５）前記（１）から（４）のいずれかに記載の方法により、真空中で無加圧焼結して内部反応により（α＋β）の二相組織を生成させたことを特徴とする、相対密度が９４％以上の二相Ｔｉ合金焼結体。
（６）前記（５）に記載の相対密度が９４％の二相Ｔｉ合金焼結体を構成要素として含むことを特徴とする構造部材。
【０００９】
次に、本発明について更に詳細に説明する。
本発明では、Ｔｉ−６Ａｌ−４Ｖ合金の焼結材に代わり、ＶをＦｅに置き換えたＴｉ−Ａｌ−Ｆｅ系合金の焼結体の開発を行った。ＶをＦｅに代替することにより、原料コストの低減と生体適合性の向上の２つの利点を得ることが可能となる。また、ＦｅはＶと同様にβ相安定化元素であるため、Ｔｉ−Ａｌ−Ｆｅ系合金は、Ｔｉ−６Ａｌ−４Ｖ合金と同じく、（α＋β）の二相合金となり、Ｔｉ−６Ａｌ−４Ｖ合金と同様に、優れた機械的特性を持つという利点が得られる。
【００１０】
これまでに、代表的なＴｉ−Ａｌ−Ｆｅ系合金として、Ｔｉ−５Ａｌ−２．５Ｆｅ合金が開発されている。本合金を焼結法で作製する場合、やはり合金粉末の入手は極めて困難であり、素粉末混合法によらざるを得ない。単純に、Ｔｉ粉、Ａｌ粉、Ｆｅ粉を混合して、成形・焼結すると、Ａｌ粉末は、元来、酸化し易く、粉末表面は、強固な酸化被膜に覆われているため、焼結・合金化が著しく阻害される。そのため、５Ａｌ−２．５Ｆｅ粉末を使用することが考えられるが、Ａｌ−Ｆｅ系状態図によると、この粉末はα−ＡｌとＦｅＡｌ_３　の２相組織であり、柔らかいα相の存在により微細な粉末に粉砕することは非常に困難である。
【００１１】
本発明では、化学量論組成のＦｅＡｌ_３　粉末のみを合金粉末組成に使用することを考えた。ＦｅＡｌ_３　は、重量比に換算すると３Ａｌ−２Ｆｅとなり、５Ａｌ−２．５Ａｌに比較的近い成分比となり、しかも、硬くて脆いため微粉化し易い上に入手することが容易であるという利点がある。また、Ｔｉ粉末とＦｅＡｌ_３粉末は、比重差が小さく、均一に混合できる利点もある。
【００１２】
【発明の実施の形態】
本発明において、原料となるＴｉ粉末は、例えば、ガスアトマイズ法、水素化脱水素（ＨＤＨ）法など、いずれの方法で製造された粉末も使用可能であるが、無加圧焼結により緻密化するため、粉末粒径の小さい方が良く、４５μｍ以下、更には、２５μｍ以下が望ましい。Ｔｉ粉末の酸素量は、０．２５ｍａｓｓ％を越えるとプロセス時に混入する酸素量を含めて、焼結体の酸素量が０．３ｍａｓｓ％以上となる恐れがあり、焼結体が著しく脆化する可能性が高くなる。そのため、Ｔｉ粉末の酸素量は、０．２５ｍａｓｓ％以下、更には、０．２０ｍａｓｓ％以下とすることが望ましい。
【００１３】
合金元素となるＦｅＡｌ_３粉末も、粒径が大きくなると焼結時の拡散による合金化が困難になるため、粒径が小さい方が良く、４５μｍ以下、更には、２０μｍ以下が望ましい。Ｔｉ粉末に対するＦｅＡｌ_３　粉末の添加量は、１ｍａｓｓ％以下では強度向上が望めず、１０ｍａｓｓ％を越えると延性が低下して脆性的に破壊する可能性が高くなるので、ＦｅＡｌ_３　の添加量は１〜１０ｍａｓｓ％の範囲が好ましい。
【００１４】
本発明の方法では、酸素量が０．２５ｍａｓｓ％以下の純Ｔｉ粉末に、金属間化合物粉末のＦｅＡｌ_３　粉末を１〜１０ｍａｓｓ％添加、混合して、必要により、バインタ−を添加、混合し、これを所定の形状に成形し、バインタ−を添加した場合は脱バインタ−処理した後、これを真空中で無加圧焼結して（α＋β）の２相Ｔｉ焼結合金を得る。本発明の上記プロセスにおいて、Ｔｉ粉末とＦｅＡｌ_３　粉末の混合方法としては、ロッキングミキサ−、Ｖ型混合機などによる乾式混合が良く、水を使った湿式混合は粉末を汚染させるためできるだけ避けるのが望ましい。
【００１５】
粉末の成形方法としては、粉末射出成形、ＣＩＰ成形、プレス成形、押出し成形などが例示されるが、これらに限定されない。成形法によっては、成形を容易、かつ確実に行うためにバインダ−を添加するが、その種類及び量は成形法により異なるため、従来から用いられているバインダ−を適切な方法で使用すれば良い。例えば、粉末射出成形法では、ワックス、熱可塑性樹脂などに、可塑剤、分散剤を配合した有機バインダ−を添加する。添加量は、コンパウンド（粉末と有機バインダ−を混合したもの）が射出成形に適正な粘度になるように、３０〜５０体積％の範囲で配合する。
【００１６】
本発明では、焼結条件として、真空中における無加圧焼結が用いられる。真空雰囲気はＴｉ粉末を酸化させないために必要である。ここで、真空度は１×１０^０　Ｐａ以下、更には１×１０^−２　Ｐａ以下が望ましい。また、無加圧焼結は、ホットプレスなどの加圧焼結とは異なり、焼結時に機械的圧力を加えないので、成形体は形状を保ったまま均一に収縮して部品形状を得ることができる。無加圧焼結の方法としては、（１）セッタ−（焼結容器）にセラミックス粉末（敷粉）を薄く敷き、その上に被焼結物を置いて焼結炉に設置する方法、（２）セッタ−に被焼結物を置き、セラミックス粉末に埋没させて焼結炉に設置する方法が例示される。
【００１７】
また、焼結体の相対密度は、９４％以上とすることが好ましい。９４％未満であると焼結体に開放気孔（焼結体表面から内部に連続する気孔）が残留し易く、焼結体の強度低下を招く恐れがある。焼結温度は１０００〜１３００℃が好ましい。焼結温度が１０００℃未満では、Ｔｉ粉末とＦｅＡｌ_３　粉末の反応が十分進まず、しかも、相対密度を９４％以上に上げることが困難となる。また、焼結温度が１３００℃を越えると、（１）粒成長により結晶粒が粗大化、（２）焼結体の酸素量の増加、の２つの要因による強度低下が懸念される。
【００１８】
次に、本発明のプロセスを、粉末射出成形法を例にとって説明すると、まず、出発原料を所定の配合比に計量した後、ロッキングミキサ−やＶ型混合機で良く乾式混合した後、ワックスや樹脂に可塑剤や分散剤を配合した有機バインダ−を３５〜５０ｖｏｌ．％添加して加熱混練を行い、射出成形用コンパウンドを作製する。次に、このコンパウンドを所定の形状の金型内に射出成形して形状付与し、グリ−ン体を得る。このグリ−ン体を加熱、溶媒抽出などの方法で脱バインダ−した後、焼結して、部品形状の焼結体を得る。
【００１９】
本発明の焼結合金は、必要な延性を維持しつつ、純Ｔｉ合金より高強度化を実現することが可能である。しかも、合金元素粉末（ＦｅＡｌ_３）の添加量を変化させることによって、強度特性を変化させることが可能である。本発明の製造プロセスでは、後記する実施例で示したように、真空中での無加圧焼結でニアネットシェイプ成形あるいはネットシェイプ成形が可能な粉末射出成形法が最も利用価値が高いプロセスである。
【００２０】
本発明の二相Ｔｉ合金焼結体は、高い強度特性を必要とする構造部材として有用であり、これらの構造部材として、例えば、生体適合性の良さと軽量性を生かした医療・生体・福祉関係の小型デバイス（内視鏡の部品、手術用道具、人工歯根など）、車いすの部品等、軽量性と質感の良さを生かした携帯用品、スポ−ツ・レジャ−用品として、腕時計のケ−ス、バンド、眼鏡フレ−ムの接続部分、釣り用品（リ−ル）、ゴルフアイアンヘッド、スキ−用品などが挙げられる。また、軽量高強度の特性を生かして、自動車エンジン部品（エンジンバルブ、コネクテンングロッド、バルブスプリングテナ−など）が例示される。これらの構造部材は、いずれも、小型部品で形状複雑な量産品ほどコストメリットが高くなり、有利である。もちろん、本発明は、粉末射出成形法に限らず、プレス成形法、ＣＩＰ成形法など諸々の粉末冶金的手法に十分応用可能である。
【００２１】
【実施例】
以下、実施例と比較例に基づいて本発明を具体的に説明するが、本発明は、以下の実施例により何ら限定されるものではない。
比較例１
ガスアトマイズ法により製造された２５μｍ以下の純Ｔｉ粉末（　酸素量０．１５ｍａｓｓ％）に、ワックスと樹脂より構成される有機バインタ−を添加し、加熱混練し、コンパウンドを作製した。有機バインタ−の添加比は体積比で３３％であった。このコンパウンドを板状引張試験片形状に射出成形し、真空中でＡｒガスを流しながら３８０℃まで脱脂した後、１０２５℃で２時間の真空焼結（１０^−３Ｐａオ−ダ−）　を行い、純Ｔｉ焼結体を作製した。
【００２２】
実施例１
比較例１で使用した純Ｔｉ粉末に、燃焼合成法により製造された２０μｍ以下のＦｅＡｌ_３　粉末を重量比で５％添加（Ｔｉ：ＦｅＡｌ_３　＝９５：５）して、ロッキングミキサ−で約１時間乾式混合して混合粉末を形成した後、ワックスと樹脂より構成される有機バインタ−を添加し、加熱混練し、コンパウンドを作製した。有機バインタ−の添加比は体積比で３５％であった。このコンパウンドを板状引張試験片形状に射出成形し、真空中でＡｒガスを流しながら３８０℃まで脱脂した後、１０５０℃で２時間の真空焼結（１０^−３Ｐａオ−ダ−）　を行い、焼結体を作製した。得られたＴｉ合金組成はＴｉ−３Ａｌ−２Ｆｅであった。
【００２３】
実施例２
実施例１のプロセスにおいて、脱脂後の焼結温度を１１００℃、２時間とした他は、実施例１と同様にして焼結体を作製した。
【００２４】
比較例２
実施例１のプロセスにおいて、脱脂後の焼結温度を９７５℃、２時間とした他は、実施例１と同様にして焼結体を作製した。
【００２５】
実施例３
実施例１のプロセスにおいて、比較例１で使用した純Ｔｉ粉末に、ＦｅＡｌ_３粉末の添加量を重量比で３％（（Ｔｉ：ＦｅＡｌ_３　＝９７：３）して、同様に焼結体を作製した。焼結温度は１０７５℃、２時間とした。得られた合金組成はＴｉ−１．８Ａｌ−１．２Ｆｅであった。
【００２６】
比較例３
実施例３のプロセスにおいて、純Ｔｉ粉末を水素化脱水素で製造された純Ｔｉ粉末（酸素量０．３０ｍａｓｓ％）に変更して、同様のプロセスで成形・焼結して焼結体を作製した。焼結温度は１１５０℃、２時間とした。
【００２７】
【表１】

【００２８】
比較例１に示す純Ｔｉ焼結体は、比較例１に示すように、破断伸びは１０％と高く、延性に富むが、０．２％耐力、引張強さは低い。これに対し、実施例１及び実施例２は、Ｔｉ−３Ａｌ−２Ｆｅ合金であるが、比較例１の純Ｔｉ焼結体に比較すると、０．２％耐力、引張強さとも大幅な向上が認められた。実施例２は、実施例１より焼結温度が高く、０．２％耐力がより向上していた。比較例２のＴｉ−３Ａｌ−２Ｆｅも合金であるが、焼結温度が低く、相対密度が９３．６％と低く、合金化も十分進んでいないため、引張特性が、実施例１、２に比較すると低下していた。実施例３は、ＦｅＡｌ_３　の添加量を減らしたＴｉ−１．８Ａｌ−１．２Ｆｅ合金であるが、０．２％耐力と引張強さはＴｉ−３Ａｌ−２Ｆｅ合金より劣るが、延性は逆に向上していた。比較例３もＴｉ−１．８Ａｌ−１．２Ｆｅ合金であるが、原料粉末のＴｉ粉末の酸素量が０．３％と高いため、脆性的に破壊し、十分な引張特性が得られなかった。
【００２９】
【発明の効果】
以上詳述したように、本発明は、焼結チタン合金及びその製造方法に係るものであり、　本発明により、粉末射出成形法などにより、引張強さ、降伏応力の高い（α＋β）二相のＴｉ合金焼結体を比較的簡単に製造し、提供することができる。また、原料コストの低減と生体適合性の向上を可能とする新しいＴｉ−Ａｌ−Ｆｅ系合金の焼結体を提供できる。上記焼結チタン合金は、優れた機械的特性をもち、各種の構造部材として有用である。
【図面の簡単な説明】
【図１】実施例１の焼結合金Ｔｉ−３Ａｌ−２Ｆｅのミクロ組織であり、灰色の部分がα相、白色の部分がβ相である。
【図２】実施例３の焼結合金Ｔｉ−ｌ．８Ａｌ−１．２Ｆｅのミクロ組織であり、灰色の部分がα相、白色の部分がβ相である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sintered titanium alloy and a method for producing the same. More specifically, the present invention relates to (α + β) having a relative density of 94% or more, which is lightweight, has high strength, high corrosion resistance, and can be produced at low cost. A) a two-phase titanium sintered alloy and a method for producing the same;
[0002]
[Prior art]
In general, titanium has excellent properties such as light weight and high corrosion resistance, and thus is expected to be used in place of iron-based materials in the fields of space and aviation equipment, transportation equipment, chemical plants, and the like. Further, because of their excellent biocompatibility, they are also being used in the medical field and in the field of ornaments worn by watches and glasses, for example. However, pure titanium containing no other elements has an α-single-phase structure and cannot be said to have high tensile strength and hardness. Therefore, (α + β) two-phase alloys including Ti-6Al-4V alloy are actually used as structural members requiring high strength characteristics.
[0003]
Heretofore, the melting casting method has been mainly used for the production of such titanium alloy members. However, this method has a technical problem since titanium has a high activity at a high temperature exceeding 1500 ° C. during melting. There are many difficult points. In addition, since titanium alloy has a higher hardness than pure titanium and is a difficult-to-process material, it is difficult to manufacture parts by machining. In order to overcome the high activity and difficult workability of the titanium alloy, research and development of a forming technology of the titanium alloy by powder metallurgy have been advanced in recent years.
[0004]
The advantages of this powder metallurgy method are that the parts are manufactured by sintering at a temperature equal to or lower than the melting point of the titanium alloy, so that handling is easy, and near-net shape molding with less post-processing after molding is possible. And excellent mechanical properties due to fine crystal grains. There are various processes in powder metallurgy, for example, press molding, CIP molding, extrusion molding, powder injection molding, etc. In any molding method, after forming into a desired shape, a sintering process is performed. Through the process of obtaining the desired shape member. In some processes, a binder is added to the powder to facilitate molding, in which case the binder is removed before sintering. Among these molding methods, a powder injection molding method is particularly effective as a technique for mass-producing complicated shaped parts.
[0005]
When a titanium alloy sintered body is manufactured by powder metallurgy, the powder used as a raw material is (1) an alloy powder method using a powder alloyed in advance with a target component, and (2) a pure titanium powder and an alloy component. Powder (a single element powder or a compound powder, or a combination thereof). Among them, the alloy powder method of the above (1) can obtain a sintered body having a uniform and stable structure and characteristics because the powder itself is alloyed, but the production of Ti alloy powder is technically difficult. Due to the difficulty, commercially available products have only a limited number of compositions and are very expensive. In particular, it is no exaggeration to say that there is almost no fine alloy powder that can be used for powder injection molding. Therefore, in order to produce a titanium alloy having a desired composition by powder metallurgy, the elemental powder mixing method (2) is almost always used.
[0006]
As a typical (α + β) two-phase Ti alloy to date, there is a Ti-6Al-4V alloy. In order to manufacture this alloy by a sintering method based on a raw powder mixing method, a Ti powder and a 60Al-40V powder are mixed at a ratio of 9: 1 (weight ratio), followed by molding and sintering. I have. However, 60Al-40V powder is very expensive and V has been pointed out to be biotoxic, and application of Ti alloys to biomaterials, which is a promising application, may be limited in the future. For this reason, in the technical field, development of a new alloy replacing Ti-6Al-4V by the powder metallurgy method was expected.
[0007]
[Problems to be solved by the invention]
Under such circumstances, the present inventors have eagerly aimed at developing a new alloy material that satisfies low cost performance and biocompatibility in place of the Ti-6Al-4V alloy in view of the conventional technology. As a result of repeated studies, they found that the intended purpose was achieved by producing a sintered body of a Ti-Al-Fe-based alloy in which V was replaced with Fe, and completed the present invention.
That is, the present invention provides a relatively simple method for producing a (α + β) two-phase Ti alloy sintered material exhibiting light weight, high strength and high corrosion resistance by powder metallurgy, particularly powder injection molding, and a product thereof. It is intended to provide.
[0008]
[Means for Solving the Problems]
The present invention for solving the above-mentioned problems includes the following technical means.
(1) 1-10 mass% of FeAl ₃ powder of an intermetallic compound is added to pure Ti powder having an oxygen content of 0.25 mass% or less and mixed to form a mixed powder. Pressureless sintering to produce a two-phase structure of (α + β) by an internal reaction, and the relative density of the sintered body is made to be 94% or more. .
(2) FeAl ₃ powder of an intermetallic compound is added to pure Ti powder having an oxygen content of 0.25 mass% or less in an amount of 1 to 10 mass% and mixed to form a mixed powder, and then the mixed powder is formed into a predetermined shape. And producing a (α + β) two-phase Ti alloy sintered body by pressureless sintering in a vacuum at a predetermined temperature so that the relative density becomes 94% or more. Method.
(3) The method according to (1) or (2), wherein the sintering temperature is 1000 to 1300 ° C.
(4) 30-50 vol. %, And the mixture is heated and kneaded, injection-molded into a predetermined shape, and then subjected to a debinding step, followed by pressureless sintering in a vacuum.
(5) The method according to any one of (1) to (4), wherein pressureless sintering is performed in a vacuum to generate a (α + β) two-phase structure by an internal reaction. A two-phase Ti alloy sintered body having a relative density of 94% or more.
(6) A structural member comprising the two-phase Ti alloy sintered body having a relative density of 94% described in (5) as a constituent element.
[0009]
Next, the present invention will be described in more detail.
In the present invention, a sintered body of a Ti-Al-Fe-based alloy in which V is replaced with Fe instead of a sintered material of a Ti-6Al-4V alloy has been developed. By substituting V for Fe, it is possible to obtain two advantages of reducing raw material costs and improving biocompatibility. Since Fe is a β-phase stabilizing element like V, the Ti-Al-Fe-based alloy becomes a two-phase alloy of (α + β) like the Ti-6Al-4V alloy, and the Ti-6Al-4V alloy The advantage of having excellent mechanical properties is obtained.
[0010]
Until now, a Ti-5Al-2.5Fe alloy has been developed as a typical Ti-Al-Fe-based alloy. When the present alloy is produced by a sintering method, it is also extremely difficult to obtain an alloy powder, and it is inevitable to use an elementary powder mixing method. When Ti powder, Al powder, and Fe powder are simply mixed and molded and sintered, the Al powder is originally easily oxidized, and the powder surface is covered with a strong oxide film. -Alloying is significantly inhibited. Therefore, it is conceivable to use 5Al-2.5Fe powder. However, according to the Al-Fe phase diagram, this powder has a two-phase structure of α-Al and FeAl ₃ , and is fine due to the presence of the soft α-phase. Grinding into a powder is very difficult.
[0011]
In the present invention, it was considered that only FeAl ₃ powder having a stoichiometric composition was used for the alloy powder composition. FeAl ₃ becomes 3Al-2Fe when converted to a weight ratio, has a component ratio relatively close to 5Al-2.5Al, and has the advantages that it is hard and brittle, is easily pulverized, and is easily available. In addition, Ti powder and FeAl ₃ powder have an advantage that the difference in specific gravity is small and uniform mixing is possible.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, as the Ti powder as a raw material, for example, a powder produced by any method such as a gas atomization method and a hydrodehydrogenation (HDH) method can be used, but the powder is densified by pressureless sintering. Therefore, the smaller the particle size of the powder, the better, and preferably 45 μm or less, and more preferably 25 μm or less. If the oxygen content of the Ti powder exceeds 0.25 mass%, the oxygen content of the sintered body, including the oxygen content mixed during the process, may be 0.3 mass% or more, and the sintered body becomes significantly embrittled. The likelihood increases. Therefore, the oxygen content of the Ti powder is desirably 0.25 mass% or less, and more desirably 0.20 mass% or less.
[0013]
When the particle size of the FeAl ₃ powder, which is an alloying element, is too large, alloying due to diffusion during sintering becomes difficult, so the smaller the particle size, the better. When the amount of FeAl ₃ powder added to Ti powder is 1 mass% or less, no improvement in strength can be expected, and when it exceeds 10 mass%, ductility decreases and the possibility of brittle fracture increases, so the amount of FeAl ₃ added is 1 mass%. The range of 10 to 10 mass% is preferable.
[0014]
In the method of the present invention, 1 to 10 mass% of an FeAl ₃ powder as an intermetallic compound powder is added to and mixed with pure Ti powder having an oxygen content of 0.25 mass% or less, and if necessary, a binder is added and mixed. This is molded into a predetermined shape, and when binder is added, after debinding, the mixture is sintered without pressure under vacuum to obtain a (α + β) two-phase Ti sintered alloy. In the above process of the present invention, as a method of mixing the Ti powder and the FeAl ₃ powder, dry mixing using a rocking mixer, a V-type mixer or the like is preferable, and wet mixing using water should be avoided as much as possible because the powder is contaminated. desirable.
[0015]
Examples of the powder molding method include, but are not limited to, powder injection molding, CIP molding, press molding, and extrusion molding. Depending on the molding method, a binder is added for easy and reliable molding, but the type and amount vary depending on the molding method, so that a conventionally used binder may be used in an appropriate method. . For example, in the powder injection molding method, an organic binder in which a plasticizer and a dispersant are blended with wax, a thermoplastic resin, or the like is added. The amount of the compound added is in the range of 30 to 50% by volume so that the compound (mixture of powder and organic binder) has a proper viscosity for injection molding.
[0016]
In the present invention, pressureless sintering in vacuum is used as a sintering condition. The vacuum atmosphere is necessary so as not to oxidize the Ti powder. Here, the degree of vacuum is preferably 1 × 10 ⁰ Pa or less, more preferably 1 × 10 ⁻² Pa or less. In addition, pressureless sintering differs from pressure sintering such as hot pressing in that no mechanical pressure is applied during sintering, so that the molded body shrinks uniformly while maintaining its shape to obtain the part shape. Can be. As a method of pressureless sintering, (1) a method in which ceramic powder (spreading powder) is thinly spread on a setter (sintering vessel), an object to be sintered is placed thereon, and then placed in a sintering furnace; 2) A method in which a material to be sintered is placed on a setter, buried in ceramic powder, and placed in a sintering furnace is exemplified.
[0017]
Further, the relative density of the sintered body is preferably set to 94% or more. If it is less than 94%, open pores (pores continuous from the surface of the sintered body to the inside) are likely to remain in the sintered body, which may cause a reduction in the strength of the sintered body. The sintering temperature is preferably from 1000 to 1300 ° C. If the sintering temperature is lower than 1000 ° C., the reaction between the Ti powder and the FeAl ₃ powder does not proceed sufficiently, and it is difficult to increase the relative density to 94% or more. If the sintering temperature exceeds 1300 ° C., there is a concern that the strength may decrease due to two factors: (1) coarsening of crystal grains due to grain growth, and (2) increase in the oxygen content of the sintered body.
[0018]
Next, the process of the present invention will be described by taking a powder injection molding method as an example. First, after the starting materials are weighed to a predetermined mixing ratio, they are thoroughly dry-mixed with a rocking mixer or a V-type mixer, and then the wax and 35-50 vol. Of an organic binder obtained by mixing a plasticizer and a dispersant with the resin. % And heat-kneaded to prepare an injection molding compound. Next, the compound is injection-molded into a mold having a predetermined shape to give a shape to obtain a green body. After removing the binder by a method such as heating or solvent extraction, the green body is sintered to obtain a component-shaped sintered body.
[0019]
The sintered alloy of the present invention can achieve higher strength than a pure Ti alloy while maintaining necessary ductility. In addition, the strength characteristics can be changed by changing the amount of the alloy element powder (FeAl ₃ ). In the manufacturing process of the present invention, the powder injection molding method capable of near-net-shape molding or net-shape molding by pressureless sintering in a vacuum is the most useful process as shown in the examples described later. is there.
[0020]
INDUSTRIAL APPLICABILITY The two-phase Ti alloy sintered body of the present invention is useful as a structural member requiring high strength characteristics. As these structural members, for example, medical / biological / welfare utilizing good biocompatibility and lightness Related small devices (endoscope parts, surgical tools, artificial dental roots, etc.), wheelchair parts, etc., portable goods that make use of light weight and good texture, sports and leisure goods, wristwatch cases Shoes, bands, eyeglass frame connections, fishing equipment (reels), golf iron heads, skiing equipment, and the like. In addition, automobile engine parts (engine valves, connecting rods, valve spring teners, etc.) are exemplified by utilizing the characteristics of light weight and high strength. All of these structural members are advantageous in that the cost merit increases as the mass-produced product becomes smaller and more complicated in shape. Of course, the present invention is not limited to the powder injection molding method, but is sufficiently applicable to various powder metallurgy techniques such as a press molding method and a CIP molding method.
[0021]
【Example】
Hereinafter, the present invention will be specifically described based on examples and comparative examples, but the present invention is not limited to the following examples.
Comparative Example 1
An organic binder composed of a wax and a resin was added to pure Ti powder (oxygen amount: 0.15 mass%) having a particle size of 25 μm or less produced by a gas atomizing method, and the mixture was heated and kneaded to prepare a compound. The addition ratio of the organic binder was 33% by volume. This compound is injection-molded into a plate-like tensile test piece, degreased to 380 ° C. while flowing Ar gas in a vacuum, and then subjected to vacuum sintering (10 ⁻³ Pa order) at 1025 ° C. for 2 hours. Then, a pure Ti sintered body was produced.
[0022]
Example 1
To the pure Ti powder used in Comparative Example 1, 5% by weight of FeAl ₃ powder of 20 μm or less produced by the combustion synthesis method was added (Ti: FeAl ₃ = 95: 5), and about 1% was added by a rocking mixer. After dry mixing for a time to form a mixed powder, an organic binder composed of a wax and a resin was added, and the mixture was heated and kneaded to prepare a compound. The addition ratio of the organic binder was 35% by volume. This compound is injection-molded into a plate-shaped tensile test piece, degreased to 380 ° C. while flowing Ar gas in a vacuum, and then subjected to vacuum sintering (10 ⁻³ Pa order) at 1050 ° C. for 2 hours. A sintered body was produced. The obtained Ti alloy composition was Ti-3Al-2Fe.
[0023]
Example 2
In the process of Example 1, a sintered body was produced in the same manner as in Example 1, except that the sintering temperature after degreasing was set to 1100 ° C. for 2 hours.
[0024]
Comparative Example 2
A sintered body was produced in the same manner as in Example 1 except that the sintering temperature after degreasing was changed to 975 ° C. for 2 hours in the process of Example 1.
[0025]
Example 3
In the process of Example 1, the amount of FeAl ₃ powder added to the pure Ti powder used in Comparative Example 1 was 3% by weight ((Ti: FeAl ₃ = 97: 3)). The sintering temperature was 1075 ° C. for 2 hours, and the obtained alloy composition was Ti-1.8Al-1.2Fe.
[0026]
Comparative Example 3
In the process of Example 3, the pure Ti powder was changed to pure Ti powder (oxygen amount: 0.30 mass%) manufactured by hydrodehydrogenation, and molded and sintered by the same process to produce a sintered body. did. The sintering temperature was 1150 ° C. for 2 hours.
[0027]
[Table 1]

[0028]
As shown in Comparative Example 1, the pure Ti sintered body shown in Comparative Example 1 has a high elongation at break of 10% and is highly ductile, but has a low 0.2% proof stress and low tensile strength. On the other hand, Examples 1 and 2 are Ti-3Al-2Fe alloys. However, compared to the pure Ti sintered body of Comparative Example 1, both the 0.2% proof stress and the tensile strength are significantly improved. Admitted. In Example 2, the sintering temperature was higher than in Example 1, and the 0.2% proof stress was further improved. Although Ti-3Al-2Fe of Comparative Example 2 is also an alloy, the sintering temperature is low, the relative density is as low as 93.6%, and the alloying is not sufficiently advanced. In comparison, it was lower. Example 3 is a Ti-1.8Al-1.2Fe alloy in which the amount of FeAl ₃ added is reduced, but the 0.2% proof stress and the tensile strength are inferior to those of the Ti-3Al-2Fe alloy, but the ductility is reversed. Had improved. Comparative Example 3 was also a Ti-1.8Al-1.2Fe alloy, but because the oxygen content of the Ti powder as the raw material powder was as high as 0.3%, it was brittlely broken, and sufficient tensile properties could not be obtained. .
[0029]
【The invention's effect】
As described above in detail, the present invention relates to a sintered titanium alloy and a method for producing the same. According to the present invention, a two-phase (α + β) having a high tensile strength and a high yield stress is obtained by a powder injection molding method or the like. A Ti alloy sintered body can be manufactured and provided relatively easily. In addition, it is possible to provide a new sintered body of a Ti-Al-Fe-based alloy that enables reduction of raw material cost and improvement of biocompatibility. The sintered titanium alloy has excellent mechanical properties and is useful as various structural members.
[Brief description of the drawings]
FIG. 1 is a microstructure of a sintered alloy Ti-3Al-2Fe of Example 1, wherein a gray portion is an α phase and a white portion is a β phase.
FIG. 2 shows a sintered alloy Ti-1. The microstructure is 8Al-1.2Fe, in which the gray part is the α phase and the white part is the β phase.

Claims

After adding 1 to 10 mass% of an intermetallic compound FeAl ₃ powder to pure Ti powder having an oxygen amount of 0.25 mass% or less and mixing to form a mixed powder, the mixed powder is formed into a green compact and is not added in vacuum. A method for producing a two-phase Ti alloy sintered body, characterized in that a two-phase structure of (α + β) is generated by an internal reaction by pressure sintering and the relative density of the sintered body is made 94% or more.

After adding 1 to 10 mass% of FeAl ₃ powder of an intermetallic compound to pure Ti powder having an oxygen content of 0.25 mass% or less and mixing to form a mixed powder, the mixed powder is formed into a predetermined shape, A method for producing a Ti sintered alloy, comprising obtaining a (α + β) two-phase Ti alloy sintered body by pressureless sintering in a vacuum at a predetermined temperature so that the density becomes 94% or more.

The method according to claim 1, wherein the sintering temperature is 1000 to 1300 ° C. 4.

An organic binder is added to the mixed powder in an amount of 30 to 50 vol. The method according to claim 2, wherein the mixture is heated and kneaded after adding the mixture, the mixture is injection-molded into a predetermined shape, and then subjected to a debindering step, and then subjected to pressureless sintering in a vacuum.

The method according to any one of claims 1 to 4, wherein pressureless sintering is performed in a vacuum to generate a (α + β) two-phase structure by an internal reaction, and the relative density is 94% or more. Two-phase Ti alloy sintered body.

A structural member comprising the two-phase Ti alloy sintered body having a relative density of 94% or more according to claim 5 as a constituent element.