JP2004238720A

JP2004238720A - Shape memory alloy

Info

Publication number: JP2004238720A
Application number: JP2003031892A
Authority: JP
Inventors: Kiyohito Ishida; 清仁石田; Ryosuke Kainuma; 亮介貝沼; Masanari Oikawa; 勝成及川; Toshihiro Omori; 俊洋大森
Original assignee: National Institute of Advanced Industrial Science and Technology AIST
Current assignee: National Institute of Advanced Industrial Science and Technology AIST
Priority date: 2003-02-10
Filing date: 2003-02-10
Publication date: 2004-08-26

Abstract

【課題】優れた加工性，耐食性を有し、Ｎｉフリー形状記憶合金を作製することもでき、かつ低温から高温まで広い温度範囲にわたって作動が可能であり、同時に、強磁性，常磁性を自由に制御できるＣｏ基形状記憶合金を提供する。
【解決手段】Ａｌを０．０１〜１１質量％，Ｓｉを０．０１〜１０質量％，Ｖを０．０１〜３２質量％，Ｇａを０．０１〜３０質量％，Ｇｅを０．０１〜２０質量％，Ｎｂを０．０１〜１０質量％，Ｔｉを０．０１〜１５質量％，Ｚｒを０．０１〜３質量％，Ｈｆを０．０１〜５質量％，Ｔａを０．０１〜１３質量％，Ｃｒを０．０１〜４０質量％，Ｗを０．０１〜４０質量％，Ｍｏを０．０１〜３０質量％，Ｓｎを０．０１〜５質量％，Ｚｎを０．０１〜４０質量％およびＢｅを０．０１〜１５質量％のうちの１種または２種以上を含有し、残部がＣｏと不可避的不純物からなる組成と、ｆｃｃ構造のγ相からなる単相組織またはγ相と異なる第２相もしくは複数の分散相からなる多相組織とを有する形状記憶合金である。
【選択図】なし[Problem] It has excellent workability and corrosion resistance, can manufacture Ni-free shape memory alloy, can operate over a wide temperature range from low to high temperature, and is free from ferromagnetism and paramagnetism. The present invention provides a Co-based shape memory alloy that can be controlled at a high speed.
SOLUTION: Al is 0.01 to 11% by mass, Si is 0.01 to 10% by mass, V is 0.01 to 32% by mass, Ga is 0.01 to 30% by mass, Ge is 0.01 to 30% by mass. 20% by mass, 0.01 to 10% by mass of Nb, 0.01 to 15% by mass of Ti, 0.01 to 3% by mass of Zr, 0.01 to 5% by mass of Hf, and 0.01 to 5% by mass of Ta. 13% by mass, Cr: 0.01 to 40% by mass, W: 0.01 to 40% by mass, Mo: 0.01 to 30% by mass, Sn: 0.01 to 5% by mass, Zn: 0.01 to 5% 40% by mass and one or more of Be in an amount of 0.01 to 15% by mass, the balance being a composition comprising Co and unavoidable impurities, and a single-phase structure or γ comprising a γ phase having an fcc structure. A shape memory alloy having a second phase different from the phase and a multiphase structure composed of a plurality of dispersed phases.
[Selection diagram] None

Description

【０００１】
【発明の属する技術分野】
本発明は、優れた延性と耐食性を有し、かつ作動温度が低温から高温まで制御可能な強磁性または常磁性形状記憶合金に関する。
【０００２】
【従来の技術】
現在、形状記憶合金は、医療用器具，携帯電話のアンテナ，メガネフレーム，パイプ継手，各種アクチュエータ等に広く用いられている。
しかし近年、その利用範囲を広げるいくつかの形状記憶合金が注目されている。従来、実用に供されてきた形状記憶合金は、その動作可能温度範囲は高々１００℃以下であり、より高温で作動可能な形状記憶合金はその利用範囲を広げるものとして期待されている。
【０００３】
また近年、アクチュエータ用材料として形状記憶合金が注目されている。これは、温度変化ではなく、磁気エネルギーを付加することによる形状変化を利用しようとするものである。これは、形状記憶効果の応答性を高めるものとして期待されている。
また形状記憶合金は、医療分野でカテーテル等に用いられるようになってきたが、生体材料であるためアレルギー性が問題となっており、特にＮｉを含まない高耐食性の形状記憶合金のニーズが高まっている。
【０００４】
ところで従来の形状記憶合金は、Ｔｉ−Ｎｉ系合金，Ｃｕ系合金，Ｆｅ系合金，Ｎｉ系合金に大別できる。そのうち、代表的なものとして、Ｔｉ−Ｎｉ合金，Ｃｕ−Ｚｎ−Ａｌ合金，Ｆｅ−Ｍｎ−Ｓｉ合金，Ｎｉ−Ｍｎ−Ｇａ合金が挙げられる。
Ｔｉ−Ｎｉ合金は、その良好な形状記憶特性のためにほぼ唯一の実用合金である。しかしコストが高く、作動温度範囲も、添加元素や加工熱処理を組み合わせても−１００〜１００ ℃と限られているため、使用用途も限られてきた。また前述のような生体材料としては、耐食性には優れるが、構成元素としてＮｉを含有するため、生体アレルギーが問題となっている。
【０００５】
Ｃｕ−Ｚｎ−Ａｌ合金は、低コストという長所を持ち、Ｔｉ−Ｎｉに換わる実用合金として注目されてきた。しかし、動作温度である逆変態温度は−１００〜１７０ ℃であるが、熱的安定性に乏しいために安定して使用できるのは４０℃までである。また、加工性や耐食性にも乏しい。
Ｆｅ−Ｍｎ−Ｓｉ合金は、トレーニング処理と呼ばれる特殊な加工熱処理を施さなければならない。これは製造コストを高くするため実用に大きな障害となる。また、その動作温度も室温〜２００ ℃である。
【０００６】
以上の合金系はすべて常磁性であり、強磁性形状記憶合金として用いることはできない。しかし近年、強磁性形状記憶合金として可能なものとしてＮｉ−Ｍｎ−Ｇａ合金が注目されている。しかし、この材料は加工性に著しく劣り、機械部品として複雑かつ精密な形状を付与するのが困難である。
【０００７】
【発明が解決しようとする課題】
以上のように、従来の形状記憶合金は実用に際して、加工性，アレルギー性，耐食性，磁気特性，作動温度範囲といった問題を抱えている。本発明は、従来にないＣｏ基の形状記憶合金であり、優れた加工性，耐食性を有し、Ｎｉフリー形状記憶合金を作製することもでき、かつ低温から高温まで広い温度範囲にわたって作動が可能であり、同時に、強磁性，常磁性を自由に制御できるといった、上記のような問題を解決できる新しい形状記憶合金を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明は、Ａｌを０．０１〜１１質量％，Ｓｉを０．０１〜１０質量％，Ｖを０．０１〜３２質量％，Ｇａを０．０１〜３０質量％，Ｇｅを０．０１〜２０質量％，Ｎｂを０．０１〜１０質量％，Ｔｉを０．０１〜１５質量％，Ｚｒを０．０１〜３質量％，Ｈｆを０．０１〜５質量％，Ｔａを０．０１〜１３質量％，Ｃｒを０．０１〜４０質量％，Ｗを０．０１〜４０質量％，Ｍｏを０．０１〜３０質量％，Ｓｎを０．０１〜５質量％，Ｚｎを０．０１〜４０質量％およびＢｅを０．０１〜１５質量％のうちの１種または２種以上を含有し、残部がＣｏと不可避的不純物からなる組成と、ｆｃｃ構造のγ相からなる単相組織またはγ相と異なる第２相もしくは複数の分散相からなる多相組織とを有する形状記憶合金である。
【０００９】
前記した発明においては、第１の好適態様として、前記組成に加えて、Ｍｎ，ＦｅおよびＮｉのうちの１種を０．０１〜４０質量％または２種以上を合計０．０１〜４０質量％含有することが好ましい。
また、第２の好適態様として、前記組成に加えて、Ｂ，Ｃ，Ｐ，Ｍｇ，Ｉｎ，Ｃｕ，Ａｇ，Ａｕ，ＰｔおよびＰｄのうちの１種を０．００１〜１０質量％または２種以上を合計０．００１〜１０質量％含有することが好ましい。
【００１０】
また、第３の好適態様として、前記記載のコバルト合金において、８００℃以上の温度で溶体化処理、または溶体化処理後さらに１００℃以上の温度で時効処理することが好ましい。
また、第４の好適態様として、前記単相または多相組織の基地相が単結晶であることが好ましい。
【００１１】
また、第５の好適態様として、前記多相組織の総体積分率が０．００１〜４０体積％の範囲内を満足することが好ましい。
【００１２】
【発明の実施の形態】
まず本発明の形状記憶合金の組成について説明する。本発明の形状記憶合金は、Ａｌを０．０１〜１１質量％，Ｓｉを０．０１〜１０質量％，Ｖを０．０１〜３２質量％，Ｇａを０．０１〜３０質量％，Ｇｅを０．０１〜２０質量％，Ｎｂを０．０１〜１０質量％，Ｔｉを０．０１〜１５質量％，Ｚｒを０．０１〜３質量％，Ｈｆを０．０１〜５質量％，Ｔａを０．０１〜１３質量％，Ｃｒを０．０１〜４０質量％，Ｗを０．０１〜４０質量％，Ｍｏを０．０１〜３０質量％，Ｓｎを０．０１〜５質量％，Ｚｎを０．０１〜４０質量％およびＢｅを０．０１〜１５質量％のうちの１種または２種以上を含有し、残部がＣｏおよび不可避的不純物からなる。さらにＭｎ，ＦｅおよびＮｉのうちの１種を０．０１〜４０質量％または２種以上を合計０．０１〜４０質量％含有することが好ましい。また、Ｂ，Ｃ，Ｐ，Ｍｇ，Ｉｎ，Ｃｕ，Ａｇ，Ａｕ，ＰｔおよびＰｄのうちの１種を０．００１〜１０質量％または２種以上を合計０．００１〜１０質量％含有することが好ましい。
【００１３】
Ｃｏは、形状記憶特性を有する元素である。しかし、純Ｃｏでは形状記憶現象が十分に発現されない。
Ａｌ，Ｓｉ，Ｖ，Ｇａ，Ｇｅ，Ｎｂ，Ｔｉ，Ｚｒ，Ｈｆ，Ｔａ，Ｃｒ，Ｗ，Ｍｏ，Ｓｎ，ＺｎおよびＢｅは、いずれも形状記憶特性を向上させる元素である。しかし、各元素とも上述の含有量を超えると、形状記憶特性の向上効果が飽和する。したがって各元素とも含有量は、上記の範囲を満足する必要がある。
【００１４】
Ｍｎ，ＦｅおよびＮｉは、いずれも形状記憶特性を向上させる元素である。しかし、これらの元素の含有量が０．０１質量％未満では形状記憶現象はほとんど向上しない。一方、これらの元素の含有量が４０質量％を超えると形状記憶特性の向上効果が飽和する。したがって、これらの元素を１種含有する場合は、その含有量は０．０１〜４０質量％の範囲内を満足し、２種以上を含有する場合は、その含有量は合計０．０１〜４０質量％の範囲内を満足する必要がある。
【００１５】
Ｂ，Ｃ，Ｐ，Ｍｇ，Ｉｎ，Ｃｕ，Ａｇ，Ａｕ，ＰｔおよびＰｄは、いずれも組織を微細化し、形状記憶特性を向上させる元素である。しかし、これらの元素の含有量が０．００１質量％未満では組織の微細化は達成されず、かつ形状記憶現象は向上しない。一方、これらの元素の含有量が１０質量％を超えると組織の微細化効果および形状記憶特性の向上効果が飽和する。したがって、これらの元素を１種含有する場合は、その含有量は０．００１〜１０質量％の範囲内を満足し、２種以上を含有する場合は、その含有量は合計０．００１〜１０質量％の範囲内を満足する必要がある。
【００１６】
次に本発明の形状記憶合金の組織について説明する。本発明の形状記憶合金は、ｆｃｃ構造のγ相からなる単相組織を有するか、またはγ相と別の第２相もしくは複数の分散相からなる多相組織を有する。
多相組織は、単相組織に比べて形状記憶特性が著しく向上するので一層好ましい。ただし、分散相の総体積分率が０．００１体積％未満では形状記憶特性の向上効果が発揮されない。一方、分散相の総体積分率が４０体積％を超えると形状記憶特性の向上効果が飽和する。したがって、分散相の総体積分率は０．００１〜４０体積％の範囲内を満足するのが好ましい。
【００１７】
本発明の形状記憶合金を製造する場合は、前記した各元素を添加して所定の成分を有する合金を不活性ガス雰囲気中で溶解する。溶解に際しては、高周波加熱溶解を採用するのが好ましい。
次いで溶解した合金を凝固鋳造させ、熱間加工および冷間加工を行ない、所定の形状に加工する。なお本発明の形状記憶合金は優れた延性を有するので、冷間加工の際に加工率４０％以上の加工が可能である。
【００１８】
所定の形状に加工した形状記憶合金を８００〜１４００℃の温度範囲で１秒〜２４時間の溶体化処理を行なう。溶体化処理後の冷却速度は特に制限はなく、水焼入れ，油焼入れ，空冷または炉冷等の従来から知られている技術を使用できる。また、後述の時効処理を行なう場合は、溶体化処理後に室温に冷却してから時効処理しても良いし、溶体化処理から直接、時効温度に冷却しても良い。このようにして形状記憶機能を付与されたｆｃｃ構造のγ相からなる単相組織またはγ相と別の第２相もしくは複数の分散相からなる多相組織を有する形状記憶合金が得られる。
【００１９】
溶体化処理後に時効処理を行なうことにより分散相を析出させても形状記憶特性は向上するので好ましい。また、時効処理後の組織が単相であっても形状記憶特性は向上するので好ましい。時効温度は１００℃以上の温度で１秒〜７２０時間の範囲内とするのが好ましい。
また、本発明の形状記憶合金は、単結晶であっても良いし、あるいは多結晶であっても良い。本発明においては、単結晶を得る方法は特定の技術に限定せず、たとえばチョクラルスキー法やブリッジマン法等の従来から知られている技術を用いれば良い。
【００２０】
【実施例】
表１に示す成分の合金を不活性ガス雰囲気中で溶製した後、平均１４０℃／ｍｉｎの冷却速度で凝固鋳造して直径２０ｍｍの鋳塊を得た。これを１２００〜１３００℃で熱間圧延し、さらに中間焼鈍を行ないながら冷間圧延した後、所定の大きさの板材を切り出した。これを１２００℃で１時間の溶体化処理後、水焼入れし、形状記憶機能を付与された多結晶形状記憶合金を製造した。これを発明例１，２，５，７，８，１１，１３とする。
【００２１】
発明例３，４，９，１０，１２，１４は、１２００℃での溶体化処理後に、さらに表１に示した時効処理を行なったものである。発明例６は、発明例５と同様の方法で多結晶形状記憶合金を製造後、さらに歪み焼きなましによって単結晶のγ相の形状記憶合金を製造した例である。ただし、このときの最終熱処理は１３００℃で１５分間とした。なお、ｆｃｃ構造のγ相中の分散相の体積分率は表２に示した。
【００２２】
比較例１は純Ｃｏであり、比較例２はＡｌの含有量が本発明の範囲を外れる例である。これらは発明例１と同様の方法で製造した。比較例２の第２相の体積分率は８０％であった。
【００２３】
【表１】

【００２４】
発明例１〜１４について、形状回復率，磁歪特性，限界冷間圧延率，Ａ_ｆ温度を調査した。その結果を表２に示す。
【００２５】
【表２】

【００２６】
形状回復率は、寸法５０ｍｍ×４ｍｍ×０．２５ｍｍの帯状の試験片で曲げ試験を行なって、１．２％の曲げ歪を与えたときの回復率を測定した。
磁歪特性は、単結晶である発明例６については寸法５ｍｍ×５ｍｍ×５ｍｍの試験片を切り出し、（１１０）面にストレンゲージを装着して、強さ３０Ａ／ｍの磁界Ｈを［００１］方向に印加して、歪量を測定した。その他の発明例および比較例１については、寸法３０ｍｍ×１０ｍｍ×１ｍｍの帯状の試験片を用い、圧延方向に平行な向きに磁場を加えたときの圧延方向の歪量を測定した。
【００２７】
なお形状記憶特性の回復率（％）は下記の（１）式で算出される値であり、磁歪特性（％）は下記の（２）式で算出される値であり、限界冷間圧延率（％）は下記の（３）式で算出される値である。
回復率（％）＝１００×（ｅ_ｄ−ｅ_ｒ）／ｅ_ｄ・・・（１）
ｅ_ｄ：変形させた後の表面歪み
ｅ_ｒ：回復させたときの表面歪み
磁歪特性（％）＝１００×（Ｌ_２−Ｌ_１）／Ｌ_１・・・（２）
Ｌ_１：磁場印加前の長さ（ｍｍ）
Ｌ_２：磁場印加後の長さ（ｍｍ）
冷間圧延率（％）＝１００×（ｔ_１−ｔ_２）／ｔ_１・・・（３）
ｔ_１：冷間圧延前の厚さ（ｍｍ）
ｔ_２：冷間圧延後の厚さ（ｍｍ）
表２から明らかなように、発明例１，２，７，８，１１を比較例１，２に比べると、形状回復率，磁歪特性，限界冷間圧延率に優れた形状記憶合金を得ることができた。また、発明例５はＢ２構造のＣｏＡｌを第２相として分散させることにより、さらに優れた形状回復率が得られる例である。また発明例４，９，１２，１４は、溶体化処理後にさらに時効処理を行なうことによりγ相中に第２相または第３相を分散させて形状記憶特性を向上させた例である。発明例３，１０は、溶体化処理後の時効処理が形状記憶特性を向上させた例である。発明例６は、単結晶において優れた磁歪特性を有していることを示している。発明例１３は常磁性形状記憶合金の例であり、適切な元素と含有量を選択することによって、常磁性，強磁性を制御できることを示している。
【００２８】
また、発明例１〜１４のＡ_ｆ温度を見ると、目的や用途に応じて低温から高温まで様々な温度で作動が可能な形状記憶合金を得ることが可能であることが分かる。
【００２９】
【発明の効果】
本発明は、新しいＣｏ基の形状記憶合金であり、優れた延性と耐食性を有し、低温から高温までの広い温度範囲にわたって作動温度を変化させることができ、かつ強磁性と常磁性を自由に制御できる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a ferromagnetic or paramagnetic shape memory alloy having excellent ductility and corrosion resistance and capable of controlling an operating temperature from a low temperature to a high temperature.
[0002]
[Prior art]
At present, shape memory alloys are widely used for medical instruments, mobile phone antennas, eyeglass frames, pipe joints, various actuators, and the like.
However, in recent years, some shape memory alloys that expand the range of use have been attracting attention. Conventionally, shape memory alloys that have been put to practical use have an operable temperature range of at most 100 ° C. or less, and shape memory alloys that can be operated at higher temperatures are expected to expand their use range.
[0003]
In recent years, shape memory alloys have attracted attention as actuator materials. This seeks to utilize not a temperature change but a shape change by applying magnetic energy. This is expected to enhance the responsiveness of the shape memory effect.
Shape memory alloys have come to be used for catheters and the like in the medical field, but are allergic because they are biomaterials. ing.
[0004]
Incidentally, conventional shape memory alloys can be broadly classified into Ti-Ni alloys, Cu alloys, Fe alloys, and Ni alloys. Among them, typical examples include Ti-Ni alloy, Cu-Zn-Al alloy, Fe-Mn-Si alloy, and Ni-Mn-Ga alloy.
Ti-Ni alloy is almost the only practical alloy due to its good shape memory properties. However, since the cost is high and the operating temperature range is limited to −100 to 100 ° C. even when the additive element and the thermomechanical treatment are combined, the usage is limited. Although the above-mentioned biomaterial is excellent in corrosion resistance, it contains Ni as a constituent element, so that bioallergy is a problem.
[0005]
Cu-Zn-Al alloys have the advantage of low cost and have attracted attention as practical alloys replacing Ti-Ni. However, the reverse transformation temperature, which is the operating temperature, is in the range of -100 to 170 ° C., but it can be used stably up to 40 ° C. due to poor thermal stability. In addition, workability and corrosion resistance are poor.
The Fe-Mn-Si alloy has to be subjected to a special thermomechanical heat treatment called a training process. This is a major obstacle to practical use because of high manufacturing costs. Also, the operating temperature is from room temperature to 200 ° C.
[0006]
All of the above alloys are paramagnetic and cannot be used as ferromagnetic shape memory alloys. However, in recent years, a Ni-Mn-Ga alloy has attracted attention as a possible ferromagnetic shape memory alloy. However, this material is extremely poor in workability, and it is difficult to give a complicated and precise shape as a mechanical part.
[0007]
[Problems to be solved by the invention]
As described above, conventional shape memory alloys have problems in practical use, such as workability, allergy, corrosion resistance, magnetic properties, and operating temperature range. The present invention is an unprecedented Co-based shape memory alloy, has excellent workability and corrosion resistance, can produce Ni-free shape memory alloy, and can operate over a wide temperature range from low to high temperatures. At the same time, it is an object of the present invention to provide a new shape memory alloy that can solve the above-mentioned problems such as the ability to freely control ferromagnetism and paramagnetism.
[0008]
[Means for Solving the Problems]
In the present invention, 0.01 to 11% by mass of Al, 0.01 to 10% by mass of Si, 0.01 to 32% by mass of V, 0.01 to 30% by mass of Ga, and 0.01 to 30% by mass of Ge. 20% by mass, 0.01 to 10% by mass of Nb, 0.01 to 15% by mass of Ti, 0.01 to 3% by mass of Zr, 0.01 to 5% by mass of Hf, 0.01 to 5% by mass of Ta. 13% by mass, Cr is 0.01 to 40% by mass, W is 0.01 to 40% by mass, Mo is 0.01 to 30% by mass, Sn is 0.01 to 5% by mass, Zn is 0.01 to 40% by mass. 40% by mass and one or more of Be in an amount of 0.01 to 15% by mass, with the balance being Co and unavoidable impurities, and a single-phase structure or γ composed of γ phase having fcc structure. A shape memory alloy having a second phase different from the phase and a multiphase structure composed of a plurality of dispersed phases.
[0009]
In the above-mentioned invention, as a first preferred embodiment, in addition to the above composition, one of Mn, Fe, and Ni is 0.01 to 40% by mass, or two or more is 0.01 to 40% by mass in total. It is preferred to contain.
As a second preferred embodiment, one of B, C, P, Mg, In, Cu, Ag, Au, Pt and Pd is added in addition to the above composition in an amount of 0.001 to 10% by mass or two types. It is preferable that the total content be 0.001 to 10% by mass.
[0010]
As a third preferred embodiment, the above-described cobalt alloy is preferably subjected to a solution treatment at a temperature of 800 ° C. or more, or an aging treatment at a temperature of 100 ° C. or more after the solution treatment.
Further, as a fourth preferred embodiment, it is preferable that the base phase of the single phase or multiphase structure is a single crystal.
[0011]
As a fifth preferred embodiment, it is preferable that the total volume fraction of the multiphase structure satisfies the range of 0.001 to 40% by volume.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the composition of the shape memory alloy of the present invention will be described. The shape memory alloy of the present invention comprises 0.01 to 11% by mass of Al, 0.01 to 10% by mass of Si, 0.01 to 32% by mass of V, 0.01 to 30% by mass of Ga, and Ge of 0.01 to 30% by mass. 0.01-20 mass%, Nb 0.01-10 mass%, Ti 0.01-15 mass%, Zr 0.01-3 mass%, Hf 0.01-5 mass%, Ta 0.01 to 13% by mass, Cr: 0.01 to 40% by mass, W: 0.01 to 40% by mass, Mo: 0.01 to 30% by mass, Sn: 0.01 to 5% by mass, Zn: It contains one or more of 0.01 to 40% by mass and 0.01 to 15% by mass of Be, and the balance consists of Co and inevitable impurities. Further, it is preferable that one of Mn, Fe and Ni is contained in an amount of 0.01 to 40% by mass or two or more of them are contained in a total of 0.01 to 40% by mass. Further, one of B, C, P, Mg, In, Cu, Ag, Au, Pt and Pd is contained in an amount of 0.001 to 10% by mass or two or more in total of 0.001 to 10% by mass. Is preferred.
[0013]
Co is an element having shape memory characteristics. However, pure Co does not sufficiently exhibit the shape memory phenomenon.
Al, Si, V, Ga, Ge, Nb, Ti, Zr, Hf, Ta, Cr, W, Mo, Sn, Zn and Be are all elements that improve shape memory characteristics. However, when the content of each element exceeds the above-mentioned content, the effect of improving the shape memory characteristics is saturated. Therefore, the content of each element must satisfy the above range.
[0014]
Mn, Fe, and Ni are all elements that improve shape memory characteristics. However, when the content of these elements is less than 0.01% by mass, the shape memory phenomenon hardly improves. On the other hand, when the content of these elements exceeds 40% by mass, the effect of improving the shape memory characteristics is saturated. Therefore, when one kind of these elements is contained, the content satisfies the range of 0.01 to 40% by mass, and when two or more kinds are contained, the content is 0.01 to 40% in total. It is necessary to satisfy the range of mass%.
[0015]
B, C, P, Mg, In, Cu, Ag, Au, Pt and Pd are all elements that refine the structure and improve the shape memory characteristics. However, if the content of these elements is less than 0.001% by mass, the microstructure is not achieved, and the shape memory phenomenon is not improved. On the other hand, when the content of these elements exceeds 10% by mass, the effect of refining the structure and the effect of improving the shape memory characteristics are saturated. Therefore, when one kind of these elements is contained, the content satisfies the range of 0.001 to 10% by mass, and when two or more kinds are contained, the content is 0.001 to 10% by mass. It is necessary to satisfy the range of mass%.
[0016]
Next, the structure of the shape memory alloy of the present invention will be described. The shape memory alloy of the present invention has a single phase structure composed of a gamma phase having an fcc structure, or has a multiphase structure composed of a gamma phase and another second phase or a plurality of dispersed phases.
The multi-phase structure is more preferable because the shape memory characteristics are significantly improved as compared with the single-phase structure. However, if the total volume fraction of the dispersed phase is less than 0.001% by volume, the effect of improving the shape memory property is not exhibited. On the other hand, when the total volume fraction of the dispersed phase exceeds 40% by volume, the effect of improving the shape memory characteristics is saturated. Therefore, the total volume fraction of the dispersed phase preferably satisfies the range of 0.001 to 40% by volume.
[0017]
When manufacturing the shape memory alloy of the present invention, the above-mentioned elements are added and the alloy having a predetermined component is melted in an inert gas atmosphere. In melting, it is preferable to employ high-frequency heating melting.
Next, the melted alloy is solidified and cast, subjected to hot working and cold working, and processed into a predetermined shape. Since the shape memory alloy of the present invention has excellent ductility, it can be worked at a working ratio of 40% or more during cold working.
[0018]
The shape memory alloy processed into a predetermined shape is subjected to a solution treatment for 1 second to 24 hours in a temperature range of 800 to 1400 ° C. The cooling rate after the solution treatment is not particularly limited, and conventionally known techniques such as water quenching, oil quenching, air cooling or furnace cooling can be used. When performing the aging treatment described below, the aging treatment may be performed after cooling to room temperature after the solution treatment, or the aging temperature may be directly cooled from the solution treatment. In this way, a shape memory alloy having a single phase structure composed of a gamma phase having an fcc structure and a multiphase structure composed of a gamma phase and another second phase or a plurality of dispersed phases to which a shape memory function is imparted is obtained.
[0019]
The aging treatment after the solution treatment is preferable because the shape memory characteristics are improved even when the dispersed phase is precipitated. Further, even if the structure after the aging treatment is a single phase, shape memory characteristics are improved, which is preferable. The aging temperature is preferably in the range of 1 second to 720 hours at a temperature of 100 ° C. or higher.
The shape memory alloy of the present invention may be a single crystal or a polycrystal. In the present invention, the method for obtaining a single crystal is not limited to a specific technique, and a conventionally known technique such as the Czochralski method or the Bridgman method may be used.
[0020]
【Example】
After smelting the alloys having the components shown in Table 1 in an inert gas atmosphere, they were solidified and cast at an average cooling rate of 140 ° C./min to obtain an ingot having a diameter of 20 mm. This was hot-rolled at 1200 to 1300 ° C., and further cold-rolled while performing intermediate annealing, after which a sheet material having a predetermined size was cut out. This was subjected to a solution treatment at 1200 ° C. for 1 hour, followed by water quenching to produce a polycrystalline shape memory alloy having a shape memory function. These are referred to as Inventive Examples 1, 2, 5, 7, 8, 11, and 13.
[0021]
Inventive Examples 3, 4, 9, 10, 12, and 14 were obtained by further performing the aging treatment shown in Table 1 after the solution treatment at 1200 ° C. Inventive Example 6 is an example in which a polycrystalline shape memory alloy was produced in the same manner as in Inventive Example 5, and then a single-crystal γ-phase shape memory alloy was produced by strain annealing. However, the final heat treatment was performed at 1300 ° C. for 15 minutes. Table 2 shows the volume fraction of the dispersed phase in the gamma phase having the fcc structure.
[0022]
Comparative Example 1 is pure Co, and Comparative Example 2 is an example in which the content of Al is out of the range of the present invention. These were produced in the same manner as in Invention Example 1. The volume fraction of the second phase in Comparative Example 2 was 80%.
[0023]
[Table 1]

[0024]
With respect to Inventive Examples 1 to 14, the shape recovery ratio, magnetostriction characteristics, critical cold rolling reduction, and _Af temperature were investigated. Table 2 shows the results.
[0025]
[Table 2]

[0026]
The shape recovery rate was determined by performing a bending test on a strip-shaped specimen having a size of 50 mm × 4 mm × 0.25 mm, and measuring a recovery rate when a bending strain of 1.2% was given.
Regarding the magnetostriction characteristics, for Invention Example 6 which is a single crystal, a test piece having a size of 5 mm × 5 mm × 5 mm was cut out, a strain gauge was attached to the (110) plane, and a magnetic field H having a strength of 30 A / m was applied in the [001] direction. To measure the amount of strain. For the other invention examples and comparative example 1, a band-shaped test piece having a size of 30 mm × 10 mm × 1 mm was used, and the amount of strain in the rolling direction when a magnetic field was applied in a direction parallel to the rolling direction was measured.
[0027]
The recovery rate (%) of the shape memory property is a value calculated by the following equation (1), and the magnetostrictive property (%) is a value calculated by the following equation (2). (%) Is a value calculated by the following equation (3).
Recovery rate _{(%) = 100 × (e} d -e r) / e d ··· (1)
_ed : surface strain after being deformed _er : surface strain when recovered (%) = 100 × (L ₂ −L ₁ ) / L ₁ (2)
L ₁ : length before applying magnetic field (mm)
L ₂ : length after application of magnetic field (mm)
Cold rolling reduction (%) = 100 × (t ₁ −t ₂ ) / t ₁ (3)
t ₁ : thickness before cold rolling (mm)
t ₂ : thickness after cold rolling (mm)
As is clear from Table 2, when the invention examples 1, 2, 7, 8, and 11 are compared with the comparative examples 1 and 2, it is possible to obtain a shape memory alloy excellent in shape recovery rate, magnetostriction characteristics, and critical cold rolling rate. Was completed. Inventive Example 5 is an example in which a more excellent shape recovery rate can be obtained by dispersing CoAl having a B2 structure as a second phase. Inventive Examples 4, 9, 12, and 14 are examples in which the aging treatment is further performed after the solution treatment to disperse the second phase or the third phase in the γ phase to improve the shape memory characteristics. Invention Examples 3 and 10 are examples in which the aging treatment after the solution treatment improved the shape memory characteristics. Invention Example 6 shows that the single crystal has excellent magnetostriction characteristics. Inventive Example 13 is an example of a paramagnetic shape memory alloy, and shows that paramagnetism and ferromagnetism can be controlled by selecting an appropriate element and content.
[0028]
Also, looking at the _Af temperatures of Invention Examples 1 to 14, it is understood that it is possible to obtain a shape memory alloy that can operate at various temperatures from low to high depending on the purpose and application.
[0029]
【The invention's effect】
The present invention is a new Co-based shape memory alloy, has excellent ductility and corrosion resistance, can change the operating temperature over a wide temperature range from low temperature to high temperature, and can freely ferromagnetic and paramagnetic. Can control.

Claims

0.01 to 11% by mass of Al, 0.01 to 10% by mass of Si, 0.01 to 32% by mass of V, 0.01 to 30% by mass of Ga, 0.01 to 20% by mass of Ge, 0.01 to 10% by mass of Nb, 0.01 to 15% by mass of Ti, 0.01 to 3% by mass of Zr, 0.01 to 5% by mass of Hf, 0.01 to 13% by mass of Ta, 0.01 to 40% by mass of Cr, 0.01 to 40% by mass of W, 0.01 to 30% by mass of Mo, 0.01 to 5% by mass of Sn, 0.01 to 40% by mass of Zn and Be contains one or more of 0.01 to 15% by mass of Be, and the balance is different from the composition comprising Co and unavoidable impurities and the single-phase structure or the γ phase comprising the γ phase having the fcc structure. A shape memory alloy having a two-phase or multi-phase structure composed of a plurality of dispersed phases.

2. The composition according to claim 1, further comprising 0.01 to 40% by mass of one of Mn, Fe, and Ni or a total of 0.01 to 40% by mass of two or more of them in addition to the composition. Shape memory alloy.

In addition to the above composition, one of B, C, P, Mg, In, Cu, Ag, Au, Pt, and Pd is 0.001 to 10% by mass or a total of two or more is 0.001 to 10% by mass. The shape memory alloy according to claim 1, wherein

The shape memory alloy according to claim 1, wherein the cobalt alloy is subjected to a solution treatment at a temperature of 800 ° C. or more, or an aging treatment at a temperature of 100 ° C. or more after the solution treatment. .

The shape memory alloy according to claim 1, wherein the base phase having a single-phase or multi-phase structure is a single crystal.

The shape memory alloy according to claim 1, 2, 3, 4, or 5, wherein a total volume fraction of the multiphase structure satisfies a range of 0.001 to 40% by volume.