JP4117375B2 - Damage control functional composite material using shape memory alloy and manufacturing method thereof - Google Patents
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【０００１】
【発明の属する技術分野】
この発明は、形状記憶合金を用いた内部損傷制御機能性複合材料の製造方法に関するものである。
さらに詳しくは、この発明は、形状記憶合金のマルテンサイト変態開始温度(Ms ）を室温以下にすることにより、マルテンサイト相状態で形状記憶合金ワイヤの予歪を発生した後、室温で形状記憶合金をオーステナイト相にさせるため、形状記憶合金ワイヤをCFRP、GFRP、エポキシ樹脂などの熱硬化性樹脂母材に埋め込み、熱硬化成形した後、一回逆変態温度以上に短時間加熱してから、室温まで冷却しても、形状記憶合金の室温で240MPa 以上の回復応力は完全に保持され、その後の加熱が必要なく、内部損傷抑制効果が常にある形状記憶合金を用いた機能性複合材料を製造する方法である。
【０００２】
【従来の技術】
従来より、予歪を与えた形状記憶合金ワイヤをCFRP、GFRP、Alなどのマトリクス中に埋め込んで、振動制御機能及び疲労亀裂進展速度を遅延させることも確認されている。これらは予め低温マルテンサイト相状態で与えた伸びひずみが、除荷のみでは歪が残留し、成形後加熱により母相に逆変態し、元の形状に回復する効果を利用している。（特許文献１〜３参照）
しかし、現在良く使っている熱処理したニチノール（Ti-50at%Ni）のマルテンサイト変態開始温度（Ms）は室温または室温以上であるため、Ti-NiワイヤをCFRP、GFRP、エポキシ樹脂などの母材に埋め込み、硬化成形して室温まで冷却すると、Ti-Ni合金の一部または全体はマルテンサイト相状態に戻るため、室温でTi-Ni合金の十分な内部損傷抑制効果が現われない。より高い温度（逆変態終了温度Af）以上に加熱しなければ、Ti-Niワイヤの十分な回復応力が得られなく、内部損傷抑制効果が利用できない。
【特許文献１】
特開平9-176330号公報
【特許文献２】
特開平6-212018号公報
【特許文献３】
特開2002-356757号公報
【０００３】
【発明が解決しようとする課題】
そこで、本発明は、形状記憶合金の組成調整と適当な熱処理により、マルテンサイトの変態開始温度（Ms）を室温以下（最大零下４０℃以下）にし、上記の欠点を解消し、室温でも形状記憶合金の十分な回復応力が得られ、わざわざ加熱しなくても内部損傷抑制効果がある機能性複合材料及びその製造方法を提供する。
【０００４】
【発明を解決するための手段】
この発明は、相変態温度を介して、オーステナイト相とマルテンサイト相があらわれる形状記憶合金を用いて、組成制御及び熱処理等によりマルテンサイト変態温度を調整し、マルテンサイト変態開始温度（Ms）を室温以下にすることにより、室温でも内部損傷制御機能がある機能性複合材料及びその製造方法を発明するに至った。
すなわち、室温以下の相変態温度を有し、相変態温度を介してオーステナイト相とマルテンサイト相が現れる形状記憶合金を用いて、室温で240MPa 以上の十分な回復応力が生じるTi-Ni系形状記憶合金ワイヤを樹脂母材で固めて成型することを特徴とする機能性複合材料を見出したものである。
【０００５】
典型的な具体例を示せば、Ti-Ni合金に一定量のＮｂを添加することにより相変態温度（Ms）が零度付近以下のTi-Ni-Nb三元合金を作製した。すなわち、 43 〜 47at ％ Ti,43 〜 47at ％ Ni, ６〜 14at ％ Nb からなるマルテンサイト変態開始温度（ M s ）が室温以下である Ti-Ni-Nb 三元系形状記憶合金を作成した。この 43 〜 47at ％ Ti,43 〜 47at ％ Ni, ６〜 14at ％ Nb からなる合金を室温で冷間延伸加工率が１０％以上、好適には３５％程度の適度な冷間加工により、形状記憶合金ワイヤの予歪を発生させると共に、この冷間延伸加工が逆変態温度 (As) を１３０℃以上に上昇させるため、形状記憶合金ワイヤをCFRP、GFRP、エポキシ樹脂などの熱硬化性樹脂母材に埋め込み、熱硬化成形する際、形状記憶合金ワイヤの予歪を保持するための装置と制御を必要とすることなしに、形状記憶合金を用いた機能性複合材料を製造した。さらに、埋め込んだ形状記憶合金を短時間加熱（通電加熱など）してから、室温までに冷却することにより、室温で240MPa 以上の形状記憶合金の収縮効果が得られる機能性複合材料を製造することができることを見出した。
【０００６】
図1は冷間加工率３５％の直径０．４ｍｍのTi-Ni-Nb合金の収縮ひずみ測定結果である。一回目の加熱では、収縮ひずみが２．４％、逆変態温度As1＝１３３．４℃、逆変態終了温度Af1＝２７６℃であることが分かった。さらに、その後の冷却では、マルテンサイト変態開始温度Ms＝−４０．４℃、終了温度Mf＝−１１１．４℃であることが分かった。この結果から、冷間加工したTi-Ni-Nb合金の変態温度範囲は非常にブロードになり、しかもマルテンサイト変態温度（MsとMf）は零下４０℃以下であり、高温から室温まで冷却してもまた母相状態になることが分かった。
また、二回目の加熱では、Ti-Ni-Nb合金の逆変態温度As＝−５２．６℃、Af＝７．５℃であることが分かった。
図２(a)はこの冷間加工したTi-Ni-Nb合金を拘束して、短時間通電加熱したときの回復応力と温度の測定結果である。通電電流は３アンペア、通電時間は１５秒である。図２(b)は温度の関数として回復応力の変化を示したものである。その結果、電流をオフして室温まで冷却しても、高温側と同じ、２８０MPaの回復応力が保持できることがはっきり分かった。
比較のために、同じ冷間加工したTi50Ni50(at%)試料を拘束して通電加熱するときの回復応力測定結果を図５(a)と(b)で示す。その結果、電流をオフして室温まで冷却すると、高温側より、回復応力が大きく減少することが分かった。
【０００７】
【発明の実施の形態】
このような研究結果を基にして、本発明の機能性複合材料及びその製造方法は考え出されたものであり、冷間加工処理した43 〜 47at ％ Ti,43 〜 47at ％ Ni, ６〜 14at ％ Nb からなるマルテンサイト変態開始温度（ M s ）が室温以下であるワイヤを用いた機能性複合材料の製造方法を以下具体的に示すことにより本発明を説明する。
本発明は、組成調整と適度な冷間加工処理により、形状記憶合金のマルテンサイト変態温度（Ms）を室温以下にし、しかも相変態温度範囲を広くする方法を提供する。本発明において、室温とは、２５℃付近の温度をいう。
さらに、これにより、形状記憶合金ワイヤをCFRP、GFRP、エポキシ樹脂などの熱硬化性樹脂母材の中に埋め込んで成形硬化した後、埋め込んだ形状記憶合金ワイヤを短時間通電加熱することにより、室温でも、常に形状記憶合金ワイヤの十分な収縮効果を利用できる機能性複合材料を製造する方法を提供する。
この埋め込んだ冷間加工状態の形状記憶合金を短時間通電加熱する理由は以下の通りである。熱硬化性樹脂母材に埋め込んで拘束したワイヤを一回逆変態させなければ、逆変態温度は正常に戻らず、回復力が利用し難いという問題がある。ところが、冷間加工した試料を逆変態させるため、逆変態終了温度まで加熱することが必要である。この温度は熱硬化性樹脂母材の硬化温度を超えるため、加熱の際、熱硬化性樹脂母材の特性に悪影響を及ぼす恐れがある。ここで、埋め込んだ形状記憶合金ワイヤを一回適度な電流で非常に短時間加熱して、逆変態を起こさせ、すぐ電流を切る。逆変態が吸熱反応であり、ワイヤ表面付近の温度がすぐ上昇しないうちに、電流を切るため、周りの熱硬化性樹脂母材に及ぼす熱の影響が小さい。開発した形状記憶合金ワイヤのマルテンサイト変態温度(Ms）は室温以下であるため、形状記憶合金ワイヤは室温まで冷却してもまだ熱硬化性樹脂母相のままであり、再び加熱しなくても240MPa 以上の回復力が得られる。
【０００８】
また、冷間加工処理はワイヤ製造過程の線引き処理だけを利用して、予歪を発生すると共に、逆変態温度を調整するため、製造コストの大幅な低減も期待できる。本発明は用いる形状記憶合金は43 〜 47at ％ Ti,43 〜 47at ％ Ni, ６〜 14at ％ Nb からなる合金である。
また、本発明で用いる樹脂母材は、代表的にはエポキシ樹脂であるが、その他フェノール樹脂やポリアミド樹脂などの熱硬化性樹脂であっても良く、強度が保てれば熱可塑性樹脂を併用しても良い。
【０００９】
【実施例】
本発明の実施例について具体的に述べる。
室温で収縮効果を保持するため、マルテンサイト変態開始温度（Ｍｓ）は室温以下になることが必要である。そのため、Ti-Ni合金の組成調整及び第三元素Nbを添加して、下記の表1に示した各組成の合金を作製した。
表1は示差走査熱量計（ＤＳＣ）及び熱膨張測定装置（ＴＭＡ）により測定した各組成の合金の相変態温度である。Ti49.5Ni50.5(at%)試料は冷間延伸加工状態と600℃で1時間処理した後測定した二種類のものである。他の各試料は冷間延伸加工状態のものを測定したものである。加工率は35％である。ここで、As1は第一回目の加熱過程で測定した逆変態開始温度、Af1は第一回目の過熱過程で測定した逆変態終了温度である。AsとAfは二回目加熱以後測定した逆変態開始と終了温度である。
その結果、Ti50Ni44Nb6(at%)組成の合金を除けば、これらの合金のマルテンサイト変態開始温度（Ms）は室温以下であることが分かった。その中、Ti45Ni46Nb9(at%)組成の合金のMs温度は最も低く、零下40℃であることがわかった。すなわち、この合金を利用することにより、零下40℃まで収縮効果が保持できることが考えられる。
以上の結果、Ti-Ni二元系の場合、Ｎｉ量が多くなると（＞＝５０．５at%）、Ms温度は室温以下に下がる。Ti-Ni合金にＮｂを添加すると、基本的にMs温度は室温以下に下がるが、その下がる具合はＮｂ、Ｔｉ，Ｎｉの量の割合による変化する。すなわち、Ｎｂ添加量の増加に伴い、Ｍｓ温度が下がる。同じＮｂ添加量の場合、Ｎｉ量はＴｉ量（原子比）より多くなる場合、Ms温度はさらに下がる。逆に、Ｎｉ量はＴｉ量（原子比）より少ない場合、Ｍｓ温度は室温以下に下がらない。
【００１０】
【表１】
また、二回目の加熱では、Ti-Ni-Nb合金の逆変態温度As＝−５３℃、Af＝７．５℃であることが分かった。
図２(a)はこの冷間加工したTi45Ni46Nb9合金を拘束して、短時間通電加熱したときの回復応力と温度の測定結果である。ここで示した温度は熱電対をワイヤ表面につけ測定したワイヤ表面温度である。通電電流は３アンペア、通電時間は１５秒である。図２(b)は温度の関数として回復応力の変化を示したものである。その結果、電流をオフして室温まで冷却しても、高温側と同じ、２８０MPaの回復応力が保持できることがはっきり分かった。
図３はＴＭＡで測定した冷間加工率３５％の直径０．４ｍｍのTi45.5Ni45.5Nb9合金ワイヤの収縮ひずみの変化である。一回目の加熱では、収縮ひずみが２．５％、逆変態温度As1＝１４５℃、逆変態終了温度Af1＝２７３℃であることが分かった。さらに、その後の冷却では、マルテンサイト変態開始温度Ms＝−２℃、終了温度Mf＝−７２℃であることが分かった。従って、この合金を高温から零下２℃まで冷却してもまた母相状態になることが分かった。
【００１１】
図４(a)と(b)はTi45.5Ni45.5Nb9合金ワイヤを通電加熱する過程中、測定した表面温度の関数として回復応力の変化である。電流をオフして室温まで冷却しても、高温側と同じ、約２４０MPaの回復応力が保持できることがはっきり分かった。
比較のために、同じ冷間加工したTi50Ni50(at%)合金ワイヤを拘束して通電加熱するときの回復応力測定結果を図５(a)と(b)で示す。その結果、電流をオフして室温まで冷却すると、高温側より、回復応力が大きく減少することが分かった。
冷間加工率３５％のTi45Ni46Nb9(at%)合金ワイヤをＣＦＲＰのプリプレグ素材層の間に入れて、ホットプレスで１３０℃２時間保持して成形硬化し、複合材料を作製した。
この成形硬化条件と同じ、冷間加工したワイヤを１３０℃２時間保持した後、短時間通電加熱して、収縮応力の変化を測定した。図６(a)と(b)はその結果を示す。これによって、１３０℃で２時間処理した冷間加工したワイヤは、一回短時間加熱した後、室温でも、約２５０MPaの収縮応力が得られることが分かった。また、以上は冷間延伸加工処理を利用して、予ひずみを与えたが、熱処理した形状記憶合金に対して、たとえば、本願の６００℃で処理したTi49.5Ni50.5合金に対して、予ひずみを与える処理を行った後、130℃或いはそれ以上の温度でCFRPのプリプレグ素材と一緒に成形硬化してから、室温で同じような収縮効果が得られる。
【００１２】
【発明の効果】
本発明は、上記の機構を採用することにより、室温でも、常に形状記憶合金の安定な240MPa 以上の回復力を利用できる機能性複合材料を熱硬化成形する事を可能にする。これによって、従来の埋め込んだ形状記憶合金を加熱することで、収縮効果を得る方法が必要なくなり、室温でも常に収縮効果がある形状記憶合金を用いた機能性複合材料を製造することが可能となる。さらに、本発明は、形状記憶ワイヤの予歪はワイヤ製造過程の冷間線引き処理だけを利用することであるため、製造コストの大幅な低減も可能にする。
【図面の簡単な説明】
【図１】 熱膨張測定（ＴＭＡ）による、冷間加工率３５％のTi45Ni46Nb9(at%)形状記憶合金ワイヤの逆変態に伴う収縮歪の変化の測定結果を示す図。
【図２】 図２(a) 冷間加工したTi45Ni46Nb9(at%)合金ワイヤを拘束した状態で、短時間通電加熱するときの回復応力とワイヤ表面温度の測定結果を示す図。通電電流は３アンペア、通電時間は２０秒である。
図２(b)冷間加工したTi45Ni46Nb9合金ワイヤを拘束した状態で加熱するとき、ワイヤ表面温度の関数として回復応力の変化を示す図。
【図３】熱膨張測定（ＴＭＡ）による、冷間加工率３５％のTi45.5Ni45.5Nb9(at%)形状記憶合金ワイヤの逆変態に伴う収縮歪の変化の測定結果を示す図。
【図４】冷間加工したTi45.5Ni45.5Nb9(at%)合金ワイヤを拘束した状態で、短時間通電加熱するときの回復応力をワイヤ表面温度の関数として示すものである。
【図５】 図５(a) 冷間加工した(冷間加工率３５％)Ｔｉ５０Ｎｉ５０（at%）合金を拘束した状態で、短時間通電加熱するときの回復応力と温度の測定結果を示す図。通電電流は２．８アンペア、通電時間は２９秒である。
図５(b) 冷間加工したＴｉ５０Ｎｉ５０合金を拘束加熱するとき、温度の関数として回復応力の変化を示す図。
【図６】 図６(a) 冷間加工したTi45Ni46Nb9(at%)合金ワイヤを１３０℃２時間処理した後、拘束した状態で、短時間通電加熱するときの回復応力と温度の測定結果を示す図。通電電流は３アンペア、通電時間は２５秒である。
図６(b) 冷間加工したTi45Ni46Nb9合金ワイヤを１３０℃２時間処理した後、拘束した状態で加熱するとき、温度の関数として回復応力の変化を示す図。
【符号の説明】
１．As：逆変態開始温度 （ただし、As1は一回目の逆変態開始温度である。）
２．Af：逆変態終了温度（ただし、Af1は一回目の逆変態開始温度である。）
３．Ms： マルテンサイト変態或いはR相変態開始温度
４．Mf：マルテンサイト変態終了温度[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an internal damage control functional composite material using a shape memory alloy.
More specifically, the present invention relates to a shape memory alloy having a shape memory at room temperature after pre-straining the shape memory alloy wire in the martensite phase state by setting the martensitic transformation start temperature (M s ) of the shape memory alloy to room temperature or lower. In order to make the alloy into the austenitic phase, the shape memory alloy wire is embedded in a thermosetting resin base material such as CFRP, GFRP, epoxy resin, and after thermosetting, it is heated once more than the reverse transformation temperature once, Even when cooled to room temperature, the recovery stress of 240 MPa or more is completely maintained at room temperature, and no subsequent heating is required, and a functional composite material using a shape memory alloy that always has an effect of suppressing internal damage is manufactured. It is a method to do.
[0002]
[Prior art]
Conventionally, it has been confirmed that a pre-strained shape memory alloy wire is embedded in a matrix of CFRP, GFRP, Al, etc. to delay the vibration control function and fatigue crack growth rate. These utilize the effect that the elongation strain previously given in the low-temperature martensite phase state remains in the unloading alone, reversely transforms into the parent phase by heating after molding, and recovers to its original shape. (See Patent Documents 1 to 3)
However, since the martensitic transformation start temperature (M s ) of heat-treated Nitinol (Ti-50at% Ni), which is often used at present, is room temperature or above room temperature, the Ti-Ni wire is made of CFRP, GFRP, epoxy resin, etc. When embedded in the material, hardened and cooled to room temperature, part or all of the Ti—Ni alloy returns to the martensite phase, and therefore the sufficient internal damage suppression effect of the Ti—Ni alloy does not appear at room temperature. Unless heating is performed at a higher temperature (reverse transformation end temperature A f ) or higher, sufficient recovery stress of the Ti—Ni wire cannot be obtained, and the internal damage suppression effect cannot be used.
[Patent Document 1]
JP-A-9-176330 [Patent Document 2]
Japanese Patent Laid-Open No. 6-212018 [Patent Document 3]
Japanese Patent Laid-Open No. 2002-356757
[Problems to be solved by the invention]
Therefore, the present invention reduces the above-mentioned drawbacks by adjusting the composition of the shape memory alloy and appropriate heat treatment, thereby lowering the martensite transformation start temperature (M s ) below room temperature (maximum below 40 ° C.). Provided are a functional composite material capable of obtaining a sufficient recovery stress of a memory alloy and having an effect of suppressing internal damage even if it is not heated.
[0004]
[Means for Solving the Invention]
This invention uses a shape memory alloy in which an austenite phase and a martensite phase appear via a phase transformation temperature, adjusts the martensite transformation temperature by composition control, heat treatment, etc., and sets the martensite transformation start temperature (M s ). By reducing the temperature to room temperature or lower, the inventors have invented a functional composite material having an internal damage control function even at room temperature and a method for manufacturing the same.
That is, has the following phase transformation temperature room, the phase transformation temperature by using austenite phase and martensite phase appears shape memory alloy through, Ti-Ni based shape memory which 240MPa or more sufficient recovery stress occurs at room temperature The present inventors have found a functional composite material characterized in that an alloy wire is solidified with a resin base material and molded.
[0005]
As a typical example, a Ti—Ni—Nb ternary alloy having a phase transformation temperature (M s ) of near zero degrees or less was prepared by adding a certain amount of Nb to a Ti—Ni alloy. That is, a Ti—Ni—Nb ternary shape memory alloy having a martensite transformation start temperature ( M s ) composed of 43 to 47 at % Ti, 43 to 47 at % Ni, and 6 to 14 at % Nb was produced at room temperature or lower . The 43 ~ 47at% Ti, 43 ~ 47at% Ni, 6~ 14at% cold stretching rate Nb composed of an alloy at room temperature is 10% or more, by moderate cold working preferably about 35%, shape memory together to generate a predistortion of the alloy wire, because this cold stretching raises the inverse transformation temperature (As) above 130 ° C., CFRP shape memory alloy wire, GFRP, thermosetting resin matrix such as epoxy resin A functional composite material using a shape memory alloy was manufactured without requiring an apparatus and control for maintaining the pre-strain of the shape memory alloy wire when embedded in thermosetting. In addition, by heating the embedded shape memory alloy for a short time (such as energization heating) and then cooling it to room temperature, a functional composite material can be produced that can obtain a shrinkage effect of the shape memory alloy of 240 MPa or more at room temperature. I found out that I can.
[0006]
FIG. 1 shows the measurement results of shrinkage strain of a Ti—Ni—Nb alloy with a diameter of 0.4 mm and a cold work rate of 35%. In the first heating, it was found that the shrinkage strain was 2.4%, the reverse transformation temperature A s1 = 133.4 ° C., and the reverse transformation end temperature A f1 = 276 ° C. Further, in the subsequent cooling, it was found that the martensite transformation start temperature M s = −40.4 ° C. and the end temperature M f = −111.4 ° C. From this result, the transformation temperature range of cold-worked Ti-Ni-Nb alloy becomes very broad, and the martensitic transformation temperature (M s and M f ) is below 40 ° C below zero, and is cooled from high temperature to room temperature. Even then, it turned out to be a parent phase.
Further, the heating of the second time, the reverse transformation temperature of Ti-Ni-Nb alloy A s = -52.6 ℃, was found to be A f = 7.5 ℃.
FIG. 2 (a) shows the measurement results of recovery stress and temperature when this cold-worked Ti—Ni—Nb alloy is constrained and heated for a short time. The energization current is 3 amperes and the energization time is 15 seconds. FIG. 2 (b) shows the change in recovery stress as a function of temperature. As a result, it was clearly found that the same recovery stress of 280 MPa as that on the high temperature side can be maintained even when the current is turned off and the system is cooled to room temperature.
For comparison, FIGS. 5 (a) and 5 (b) show the results of measurement of recovery stress when the same cold-worked Ti50Ni50 (at%) sample is restrained and energized and heated. As a result, it was found that when the current was turned off and cooled to room temperature, the recovery stress was greatly reduced from the high temperature side.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
And such findings based, functional composite material and its manufacturing method of the present invention has been conceived, cold working processed 43 ~ 47at% Ti, 43 ~ 47at% Ni, 6~ 14at The present invention will be described by specifically showing a method for producing a functional composite material using a wire having a martensite transformation start temperature ( M s ) composed of % Nb and having a room temperature or less .
The present invention provides a method for reducing the martensitic transformation temperature (M s ) of a shape memory alloy to room temperature or lower and widening the phase transformation temperature range by adjusting the composition and appropriate cold working. In the present invention, room temperature refers to a temperature around 25 ° C.
In addition, after this, the shape memory alloy wire is embedded in a thermosetting resin base material such as CFRP, GFRP, epoxy resin, etc. and cured, and then the embedded shape memory alloy wire is heated at room temperature for a short time. However, the present invention provides a method for producing a functional composite material that can always use the sufficient shrinkage effect of the shape memory alloy wire.
The reason why the embedded shape memory alloy in the cold worked state is heated for a short time is as follows. If the wire embedded and restrained in the thermosetting resin base material is not reverse transformed once, there is a problem that the reverse transformation temperature does not return to normal and the recovery force is difficult to use. However, in order to reversely transform a cold-worked sample, it is necessary to heat it to the reverse transformation end temperature. This temperature is to exceed the curing temperature of the thermosetting resin matrix, upon heating, it can adversely affect the properties of the thermosetting resin matrix. Here, the embedded shape memory alloy wire is heated once with a moderate current for a very short time to cause reverse transformation, and the current is immediately turned off. The reverse transformation is an endothermic reaction, and since the current is cut before the temperature near the wire surface immediately rises, the influence of heat on the surrounding thermosetting resin base material is small. Since the developed shape memory alloy wire has a martensite transformation temperature (M s ) of room temperature or less, the shape memory alloy wire is still a thermosetting resin matrix even when cooled to room temperature. The recovery power of 240MPa or more can be obtained.
[0008]
In addition, since the cold working process uses only the wire drawing process in the wire manufacturing process to generate pre-strain and to adjust the reverse transformation temperature, a significant reduction in manufacturing cost can be expected. The present invention utilizes shape memory alloy is 43 ~ 47at% Ti, 43 ~ 47at% Ni, alloy consisting. 6 to 14 at% Nb.
The resin base material used in the present invention is typically an epoxy resin, but may be a thermosetting resin such as a phenol resin or a polyamide resin. If the strength is maintained, a thermoplastic resin is used in combination. Also good.
[0009]
【Example】
Examples of the present invention will be specifically described.
For holding the contraction effect at room temperature, the martensite transformation start temperature (M s) is required to be less than or equal to room temperature. Therefore, the composition adjustment of the Ti—Ni alloy and the third element Nb were added to prepare alloys having the respective compositions shown in Table 1 below.
Table 1 shows the phase transformation temperatures of the alloys of each composition measured by a differential scanning calorimeter (DSC) and a thermal expansion measuring device (TMA). Ti49.5Ni50.5 (at%) samples are of two types measured after cold-drawing and after 1 hour treatment at 600 ℃. The other samples were measured in the cold stretched state. The processing rate is 35%. Here, A s1 is the reverse transformation start temperature measured in the first heating process, and A f1 is the reverse transformation end temperature measured in the first overheating process. A s and A f are the reverse transformation start and end temperatures measured after the second heating.
As a result, it was found that the martensitic transformation start temperature (M s ) of these alloys was not more than room temperature except for alloys having a Ti50Ni44Nb6 (at%) composition. Wherein, Ti45Ni46Nb9 (at%) M s temperature of the alloy composition has the lowest was found to be below zero 40 ° C.. That is, it is conceivable that the shrinkage effect can be maintained up to 40 ° C. by using this alloy.
As a result, in the case of the Ti—Ni binary system, when the amount of Ni increases (> = 50.5 at%), the M s temperature decreases to room temperature or lower. When Nb is added to the Ti—Ni alloy, the M s temperature is basically lowered to room temperature or lower, but the degree of decrease varies depending on the ratio of the amounts of Nb, Ti, and Ni. That is, with the increase of the addition amount of Nb, M s temperature decreases. In the case of the same Nb addition amount, when the Ni amount becomes larger than the Ti amount (atomic ratio), the Ms temperature further decreases. Conversely, Ni amount is less than the amount of Ti (atomic ratio), M s temperature does not decrease below room temperature.
[0010]
[Table 1]
Further, the heating of the second time, the reverse transformation temperature of Ti-Ni-Nb alloy A s = -53 ° C., was found to be A f = 7.5 ℃.
FIG. 2 (a) shows the measurement results of recovery stress and temperature when this cold-worked Ti45Ni46Nb9 alloy is constrained and heated for a short time. The temperature shown here is the wire surface temperature measured by attaching a thermocouple to the wire surface. The energization current is 3 amperes and the energization time is 15 seconds. FIG. 2 (b) shows the change in recovery stress as a function of temperature. As a result, it was clearly found that the same recovery stress of 280 MPa as that on the high temperature side can be maintained even when the current is turned off and the system is cooled to room temperature.
FIG. 3 shows a change in shrinkage strain of a Ti45.5Ni45.5Nb9 alloy wire having a diameter of 0.4 mm and a cold working rate of 35% measured by TMA. In the first heating, it was found that the shrinkage strain was 2.5%, the reverse transformation temperature A s1 = 145 ° C., and the reverse transformation end temperature A f1 = 273 ° C. Furthermore, in subsequent cooling, it turned out that it is martensitic transformation start temperature Ms = -2 degreeC and end temperature Mf = -72 degreeC. Therefore, it has been found that even when this alloy is cooled from high temperature to below 2 ° C., it becomes a parent phase again.
[0011]
4 (a) and 4 (b) show the change in recovery stress as a function of the measured surface temperature during the process of energizing and heating the Ti45.5Ni45.5Nb9 alloy wire. It was clearly found that even when the current was turned off and cooled to room temperature, the same recovery stress of about 240 MPa as that on the high temperature side could be maintained.
For comparison, FIGS. 5 (a) and 5 (b) show the results of measurement of recovery stress when the same cold-worked Ti50Ni50 (at%) alloy wire is restrained and energized and heated. As a result, it was found that when the current was turned off and cooled to room temperature, the recovery stress was greatly reduced from the high temperature side.
A Ti45Ni46Nb9 (at%) alloy wire having a cold work rate of 35% was placed between CFRP prepreg material layers, and held at 130 ° C. for 2 hours with a hot press to be molded and cured to produce a composite material.
A cold-worked wire having the same molding and hardening conditions as above was held at 130 ° C. for 2 hours, and then heated for a short time to measure changes in shrinkage stress. FIGS. 6A and 6B show the results. As a result, it was found that the cold-worked wire treated at 130 ° C. for 2 hours can obtain a contraction stress of about 250 MPa even at room temperature after being heated once for a short time. In addition, the pre-strain was applied by using the cold drawing process, but for the heat-treated shape memory alloy, for example, for the Ti49.5Ni50.5 alloy processed at 600 ° C. After the treatment for imparting strain, the same shrinkage effect can be obtained at room temperature after molding and curing together with the CFRP prepreg material at a temperature of 130 ° C. or higher.
[0012]
【The invention's effect】
By adopting the above-described mechanism, the present invention makes it possible to thermoset and mold a functional composite material that can always use a stable recovery force of 240 MPa or more of a shape memory alloy even at room temperature . This eliminates the need for a method for obtaining a shrinkage effect by heating a conventional embedded shape memory alloy, and makes it possible to produce a functional composite material using a shape memory alloy that always has a shrinkage effect even at room temperature. . Furthermore, the present invention also enables a significant reduction in manufacturing cost since the pre-straining of the shape memory wire uses only the cold drawing process in the wire manufacturing process.
[Brief description of the drawings]
FIG. 1 is a diagram showing measurement results of changes in shrinkage strain associated with reverse transformation of a Ti45Ni46Nb9 (at%) shape memory alloy wire having a cold work rate of 35%, by thermal expansion measurement (TMA).
FIG. 2 (a) is a view showing measurement results of recovery stress and wire surface temperature when a cold-worked Ti45Ni46Nb9 (at%) alloy wire is constrained and heated for a short time. The energization current is 3 amps and the energization time is 20 seconds.
FIG. 2 (b) shows the change in recovery stress as a function of wire surface temperature when cold-worked Ti45Ni46Nb9 alloy wire is heated in a restrained state.
FIG. 3 is a diagram showing measurement results of changes in shrinkage strain associated with reverse transformation of a Ti45.5Ni45.5Nb9 (at%) shape memory alloy wire having a cold work rate of 35% by thermal expansion measurement (TMA).
FIG. 4 shows the recovery stress as a function of the wire surface temperature when a cold worked Ti45.5Ni45.5Nb9 (at%) alloy wire is constrained and heated for a short time.
FIG. 5 (a) is a graph showing measurement results of recovery stress and temperature when a cold-worked (cold work rate of 35%) Ti50Ni50 (at%) alloy is constrained and heated for a short time. . The energization current is 2.8 amperes and the energization time is 29 seconds.
FIG. 5B is a diagram showing a change in recovery stress as a function of temperature when cold-worked Ti50Ni50 alloy is restrained and heated.
FIG. 6 (a) shows measurement results of recovery stress and temperature when cold-worked Ti45Ni46Nb9 (at%) alloy wire is treated at 130 ° C. for 2 hours and then energized and heated for a short time. Figure. The energization current is 3 amperes and the energization time is 25 seconds.
FIG. 6B is a diagram showing a change in recovery stress as a function of temperature when a cold-worked Ti45Ni46Nb9 alloy wire is heated at 130 ° C. for 2 hours and then heated in a restrained state.
[Explanation of symbols]
1. A s : Reverse transformation start temperature (However, A s1 is the first reverse transformation start temperature.)
2. A f : reverse transformation end temperature (where A f1 is the first reverse transformation start temperature)
3. M s : Martensitic transformation or R phase transformation start temperature M f: martensitic transformation finish temperature
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