JP3907177B2 - Fe-based shape memory alloy and manufacturing method thereof - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は実用温度域での優れた形状記憶特性、加工性及び耐食性を有する低廉なFe基形状記憶合金及びその製造方法に関する。
【０００２】
【従来の技術】
形状記憶合金は、各種工業、医療等の分野で、その特異的な機能を利用すべく実用化が進められている。形状記憶現象及び超弾性現象（擬弾性現象ともいう）は熱弾性マルテンサイト変態を起こす合金に現れるものであり、このような合金として、Ni-Ti系合金、Ni-Al系合金、Cu-Zn-Al系合金、Cu-Al-Ni系合金等の非鉄系合金と、Fe-Ni-Co-Ti系合金、Fe-Mn-Si系合金、Fe-Ni-C系合金、Fe-Ni-Cr系合金等の鉄系合金とが知られている。
【０００３】
【発明が解決しようとする課題】
しかし実用化されているのは主に非鉄系合金であり、Fe基形状記憶合金にはまだ解決されていないさまざまな問題がある。例えばFe-Ni-Co-Ti系合金は応力誘起変態による形状記憶効果を示すが、Ms点（マルテンサイト変態開始温度）が200 K以下と低い。Fe-Ni-C系合金では逆変態中に炭化物が生成し、そのため形状記憶性が低下する。Fe-Mn-Si系合金は比較的良好な形状記憶特性を示すが、冷間加工性が悪く、加工にコストがかかる上、耐食性が不充分であり、実用化できる分野が限られている。
【０００４】
上記問題点にもかかわらず、Fe基形状記憶合金には原料コストが低く、磁性を示す等の利点があるため、より実用的なFe基形状記憶合金の開発が望まれている。
【０００５】
従って、本発明の目的は、実用温度域での優れた形状記憶特性、加工性及び耐食性を有する低廉なFe基形状記憶合金及びその製造方法を提供することである。
【０００６】
【課題を解決するための手段】
上記目的に鑑み鋭意研究の結果、本発明者らは、所定量のNi及びAlをFeに添加することにより、実用温度域での優れた形状記憶特性及び加工性を有するFe基形状記憶合金が得られることを見出し、本発明に想到した。
【０００７】
すなわち、本発明の第１のFe基形状記憶合金は、15〜40質量％のNiと、1.5〜10質量％のAlとを含有し、残部がFe及び不可避的不純物からなるFe-Ni-Al 系合金を 800 ℃以上の温度で溶体化処理した後、 200 ℃以上〜 800 ℃未満の温度で時効処理してなることを特徴とする。
【０００８】
本発明の第２のFe基形状記憶合金は、15〜40質量％のNiと、1.5〜10質量％のAlと、30質量％以下のCoとを含有し、残部がFe及び不可避的不純物からなるFe-Ni-Al 系合金を 800 ℃以上の温度で溶体化処理した後、 200 ℃以上〜 800 ℃未満の温度で時効処理してなることを特徴とする。
【０００９】
本発明の第３のFe基形状記憶合金は、15〜40質量％のNiと、1.5〜10質量％のAlとを含有し、さらにTi 、 B 又は Cr を0.001〜15質量％含有し、残部がFe及び不可避的不純物からなるFe-Ni-Al 系合金を 800 ℃以上の温度で溶体化処理した後、 200 ℃以上〜 800 ℃未満の温度で時効処理してなることを特徴とする。
【００１０】
本発明の第４のFe基形状記憶合金は、15〜40質量％のNiと、1.5〜10質量％のAlと、30質量％以下のCoとを含有し、さらに0.001 〜 15 質量％の Ta 又は 0.001 質量％以上〜 1.5 質量％未満の Si を含有し、残部がFe及び不可避的不純物からなるFe-Ni-Al 系合金を 800 ℃以上の温度で溶体化処理した後、 200 ℃以上〜 800 ℃未満の温度で時効処理してなることを特徴とする。
【００１１】
上記第１〜４のFe基形状記憶合金はいずれもNi3Al等のfcc及び／又はfct構造を有する規則相を含有するのが好ましい。これにより形状記憶特性が向上する。
【００１２】
本発明の第１のFe基形状記憶合金の製造方法は、15〜40質量％のNiと、1.5〜10質量％のAlとを含有し、残部がFe及び不可避的不純物からなるFe-Ni-Al系合金を800℃以上の温度で溶体化処理した後、 200 ℃以上〜 800 ℃未満の温度で時効処理することを特徴とする。
【００１３】
本発明の第２のFe基形状記憶合金の製造方法は、15〜40質量％のNiと、1.5〜10質量％のAlと、30質量％以下のCoとを含有し、残部がFe及び不可避的不純物からなるFe-Ni-Al系合金を800℃以上の温度で溶体化処理した後、 200 ℃以上〜 800 ℃未満の温度で時効処理することを特徴とする。
【００１４】
本発明の第３のFe基形状記憶合金の製造方法は、15〜40質量％のNiと、1.5〜10質量％のAlとを含有し、さらにTi 、 B 又は Cr を0.001〜15質量％含有し、残部がFe及び不可避的不純物からなるFe-Ni-Al系合金を800℃以上の温度で溶体化処理した後、 200 ℃以上〜 800 ℃未満の温度で時効処理することを特徴とする。
【００１５】
本発明の第４のFe基形状記憶合金の製造方法は、15〜40質量％のNiと、1.5〜10質量％のAlと、30質量％以下のCoとを含有し、さらに0.001 〜 15 質量％の Ta 又は 0.001 質量％以上〜 1.5 質量％未満の Si を0.001〜15質量％含有し、残部がFe及び不可避的不純物からなるFe-Ni-Al系合金を800℃以上の温度で溶体化処理した後、 200 ℃以上〜 800 ℃未満の温度で時効処理することを特徴とする。
【００１６】
上記第１〜４のFe基形状記憶合金の製造方法において、溶体化処理の後、さらに200℃以上〜800℃未満の温度で時効処理することによりNi3Al等のfcc及び／又はfct構造を有する規則相が析出する。
【００１７】
【発明の実施の形態】
[1] Fe-Ni-Al系合金の組成
(a) 基本組成
本発明のFe基形状記憶合金を構成するFe-Ni-Al系合金の基本組成は、15 〜40質量％のNiと、1.5 〜10質量％のAlとを含有し、残部はFeと不可避的不純物とからなる。なお本明細書において、特段の断りがなければ各元素の含有量は合金全体を基準（100質量％）とする。
【００１８】
Niを含有することにより、Fe基形状記憶合金のマルテンサイト変態温度が下がり、母相（fcc相）が安定化する。Niの含有量を15質量％未満にすると板状マルテンサイト組織が生成しない。一方40質量％超にするとマルテンサイト変態温度が低下し過ぎ、実用温度域で変態が現れないため、良好な形状記憶特性が得られない。好ましいNiの含有量は20 〜38質量％である。
【００１９】
Alを含有することにより、後述する時効処理によってNi3Al等のfcc及び／又はfct構造を有する規則相が析出する。Fe基形状記憶合金が上記規則相を含有することにより、母相が強化されるとともに形状記憶特性が向上する。Alの含有量はNiの含有量によって変化するが、２ 〜８質量％であるのが好ましく、３ 〜８質量％であるのがより好ましい。
【００２０】
(b) 基本組成以外の元素
Fe-Ni-Al系合金は、上記基本組成以外にCo元素を含有するのが好ましい。Coを含有することにより、母相の剛性率が低下して変態歪みが減少し、その結果形状記憶特性が向上する。Coの含有量は30質量％以下であるのが好ましく、0.01 〜15質量％であるのがより好ましい。Coの含有量が30質量％を超えると、合金の冷間加工性が低下する恐れがある。
【００２１】
Fe-Ni-Al系合金は、さらにBe、Cu、V、Mo、W、Nb、Ti、Zr、Ta、C、B、Cr、Mn、Hf、Re、Y、Ru、Ir、Ga、Si及びGeからなる群から選ばれた少なくとも一種を含有することができる。これらの元素の含有量は合計で0.001 〜15質量％であるのが好ましく、0.001 〜12質量％であるのがより好ましく、0.001 〜10質量％であるのがさらに好ましい。これらの元素は、結晶粒を微細化してFe基形状記憶合金の強度を上げる効果を有する。但しこれら元素の合計含有量が15質量％を超えると合金が脆化する恐れがある。
【００２２】
Be又はCuを添加することにより固溶強化が起こって母相の強度が上がり、形状記憶特性が向上する。Be及びCuの好ましい含有量は１質量％以下である。
【００２３】
Ti、Zr、Ta、V、Mo、W、Nb、Hf、Re、Ru、Ir、Ga、Si及びGeは母相の積相欠陥エネルギーを低下させ、板状マルテンサイト組織を生成しやすくする元素である。またこれらの元素はNiとの金属間化合物相を析出して母相を強化する作用を有する。Ti、Zr、Ta、V、Mo、W、Nb、Hf、Re、Ru、Ir、Ga、Si及びGeの好ましい含有量は10質量％以下である。Siのより好ましい含有量は0.001質量％以上 〜1.5質量％未満である。またTiのより好ましい含有量は0.001質量％以上 〜2.5質量％未満である。
【００２４】
BをTiとともに添加することにより、結晶組織の微細化効果が向上する。Bの好ましい含有量は１質量％以下である。
【００２５】
Cを添加することによりマルテンサイト組織の変態歪みが減少し、形状記憶特性が向上するとともにMs点が低下するので、比較的高価なNiの含有量を減らすことができる。Cの好ましい含有量は１質量％以下である。またCをTiとともに添加することによりTiCが析出し、結晶組織の微細化効果が向上する。
【００２６】
Cr及びYは耐摩耗性及び耐食性を維持するのに有効な元素である。Cr及びYの好ましい含有量は10質量％以下である。
【００２７】
Mnを添加することによりMs点が低下するので、比較的高価なNiの含有量を減らすことができる。Mnの好ましい含有量は５質量％以下である。
【００２８】
[2] Fe基形状記憶合金の製造方法
(a) Fe-Ni-Al系合金の成形
上記組成のFe-Ni-Al系合金を溶解鋳造し、熱間加工（熱間圧延等）、冷間加工（冷間圧延等）、プレス等の加工により所望の形状に成形する。上記組成のFe-Ni-Al系合金は熱間加工性及び冷間加工性に富み、極細線、箔等各種形状に容易に成形することができる。
【００２９】
(b) 溶体化処理
次に固溶体温度範囲まで加熱し、結晶組織をオーステナイト（fcc相）に変態させた後、急冷する溶体化処理を行う。溶体化処理は800 ℃以上の温度で行う。処理温度は900 〜1400 ℃であるのが好ましい。処理温度での保持時間は0.1分以上であれば良いが、60分を超えると酸化の影響が無視できなくなるので、0.1 〜60分であるのが好ましい。加熱処理後、50 ℃／秒以上の速度で急冷することにより、マルテンサイト組織が得られる。冷却速度を50 ℃／秒未満にすると、β相（B2構造のβ相）が析出してしまい、形状記憶性が得られない。好ましい冷却速度は200 ℃／秒以上である。急冷は水等の冷媒に入れるか、又は強制空冷により行う。
【００３０】
(c) 時効処理
溶体化処理のみでも良好な形状記憶特性は得られるが、時効処理を行うことにより、Ni3Al等のfcc及び／又はfct構造を有する規則相が現れ、母相が強化されるとともに、形状記憶特性が向上するので好ましい。時効処理は200 ℃以上 〜800 ℃未満の温度で行う。200 ℃未満で処理すると、上記規則相の析出が不十分となる。一方800 ℃以上で処理すると、安定相であるβ相が析出する。
【００３１】
時効処理時間はFe基形状記憶合金の組成及び処理温度により異なるが、１分間以上であるのが好ましく、30分間 〜100時間であるのがより好ましい。時効処理時間が１分間未満では効果が不十分である。一方時効処理時間を無用に長くすると（例えば数百時間）、β相が析出して形状記憶性が消失する恐れがある。
【００３２】
[3] Fe基形状記憶合金の特性
本発明のFe基形状記憶合金は、板状マルテンサイト組織を有し、実用温度域で安定かつ良好な形状記憶特性及び超弾性を有する。特に時効処理した場合には形状回復率は概ね30％以上であり、さらにCoを含有する場合には概ね50％以上である。また降伏応力（0.2％耐力）は概ね250 MPa以上であり、特に時効処理した場合には概ね450 MPa以上である。さらに本発明のFe基形状記憶合金は良好な硬度、引張強度及び破断伸びを有するため、加工性に優れている。
【００３３】
【実施例】
本発明を以下の実施例によりさらに詳細に説明するが、本発明はこれらの例に限定されるものではない。
【００３４】
実施例１
表１に示すサンプル１〜13の組成を有するFe-Ni-Al系合金を溶解し、140 ℃／分の冷却速度で凝固して、直径20 mm×長さ120 mmの円柱状鋳塊を作製した。この鋳塊を1200 ℃で４倍に熱間圧延し、次いで10倍に冷間圧延して、厚さ0.2 mmの板材を作製した。各板材を1300 ℃で10分間加熱処理した後、氷水中へ投入して急冷した（溶体化処理）。次いで600 ℃で時効処理を行い、Fe基形状記憶合金の板状サンプルを得た。時効処理時間は表１に示す通りである。
【００３５】
【表１】
得られた各板材の物性を以下の方法で測定した。測定結果を表２及び表３に示す。
【００３７】
(1) 硬さ（ビッカーズ硬度）
マイクロビッカーズ硬度計（（株）明石製作所製MVK-H1）を用いた。
(2) 形状回復率
各板材を液体窒素中で直径10 mmの丸棒に巻きつけ、液体窒素から取り出し、曲がった状態での曲率半径R0 を測定した。次に曲がった板材を600 ℃に加熱し、形状回復を起こさせた後の曲率半径R1 を測定し、次式：
形状回復率（％）＝100 ×（R1−R0）／R1
により、形状回復率を算出した。
(3) 引張試験
JIS Z 2241に準拠し、引張強さ、破断伸び及び降伏応力（0.2％耐力）を求めた。
【００３８】
【表２】
【表３】
表２及び表３からわかるように、サンプル１〜13のいずれもが良好な形状記憶特性を示した。特にCo元素を含有するサンプル４〜10は、Coを含有しない板材に比べて高い形状回復率を示した。また時効処理を行ったサンプル２、３、５、６、７、８、９、10、11、12及び13は、時効処理を行わなかった板材に比べて形状回復率が著しく向上しているとともに、ビッカーズ硬度、引張強さ及び降伏応力も向上していることがわかる。サンプル５の板材を光学顕微鏡で観察したところ（図１参照、80倍）、板状のマルテンサイト組織が生成しているのが観察された。
【００４１】
実施例２
表１に示すサンプル４と同じ組成のFe-Ni-Al系合金を実施例１と同じ方法で板材に成形し、実施例１と同じ条件で溶体化処理（焼入れ）した後、600 ℃で０時間、４時間、13時間、36時間及び100時間の各時効処理を行った。得られた各板材の形状回復率及びビッカーズ硬度を実施例１と同じ方法で測定した。結果を図２に示す。図２から明らかなように、溶体化処理（焼入れ）のみの板材の形状回復率は10％未満であり、ビッカーズ硬度も低いが、時効処理時間が長くなるにつれて、形状回復率及びビッカーズ硬度ともに著しく向上した。また時効処理を36時間行った板材を透過型電子顕微鏡で観察したところ（図３参照、160,000倍）、数nm径の微細なfcc規則相が析出していることが分かった。
【００４２】
【発明の効果】
以上詳述した通り、本発明のFe基形状記憶合金は、実用温度域で安定かつ良好な形状記憶特性を有する。さらに本発明のFe基形状記憶合金はFe-Ni-Al系合金からなるため材料コストが低い上、加工性及び耐食性に優れるため、線材、板材、箔及びパイプ等多様な形状の製品を安価に製造することができる。
【図面の簡単な説明】
【図１】 実施例１のサンプル５のFe基形状記憶合金板材の板状マルテンサイト組織を示す光学顕微鏡写真である。
【図２】 実施例２における時効処理時間と形状回復率及びビッカーズ硬度との関係を示すグラフである。
【図３】 実施例２において時効処理を36時間行ったFe基形状記憶合金板材の透過型電子顕微鏡写真である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inexpensive Fe-based shape memory alloy having excellent shape memory characteristics, workability and corrosion resistance in a practical temperature range, and a method for producing the same.
[0002]
[Prior art]
Shape memory alloys are being put to practical use in order to utilize their specific functions in various industrial and medical fields. Shape memory phenomenon and superelastic phenomenon (also called pseudoelastic phenomenon) appear in alloys that undergo thermoelastic martensitic transformation, such as Ni-Ti alloys, Ni-Al alloys, Cu-Zn Non-ferrous alloys such as Al-Al alloys and Cu-Al-Ni alloys, Fe-Ni-Co-Ti alloys, Fe-Mn-Si alloys, Fe-Ni-C alloys, Fe-Ni-Cr Iron-based alloys such as alloy are known.
[0003]
[Problems to be solved by the invention]
However, nonferrous alloys are mainly put into practical use, and there are various problems that have not yet been solved for Fe-based shape memory alloys. For example, Fe-Ni-Co-Ti alloys show a shape memory effect due to stress-induced transformation, but the Ms point (martensitic transformation start temperature) is as low as 200 K or less. In Fe-Ni-C alloys, carbides are generated during reverse transformation, which reduces shape memory properties. Fe-Mn-Si alloys exhibit relatively good shape memory characteristics, but have poor cold workability, are costly to work, have insufficient corrosion resistance, and have limited fields for practical use.
[0004]
In spite of the above problems, Fe-based shape memory alloys have advantages such as low raw material costs and magnetism. Therefore, development of more practical Fe-based shape memory alloys is desired.
[0005]
Accordingly, an object of the present invention is to provide an inexpensive Fe-based shape memory alloy having excellent shape memory characteristics, workability and corrosion resistance in a practical temperature range, and a method for producing the same.
[0006]
[Means for Solving the Problems]
As a result of diligent research in view of the above object, the present inventors have obtained a Fe-based shape memory alloy having excellent shape memory characteristics and workability in a practical temperature range by adding a predetermined amount of Ni and Al to Fe. The inventors have found out that the present invention can be obtained and have arrived at the present invention.
[0007]
That is, the first Fe-based shape memory alloy of the present invention contains 15 to 40% by mass of Ni and 1.5 to 10% by mass of Al, with the balance being Fe-Ni-Al composed of Fe and inevitable impurities. after solution treatment the system alloy at 800 ° C. or higher temperatures, is characterized by being aged at a temperature of less than ~ 800 ° C. 200 ° C. or higher.
[0008]
The second Fe-based shape memory alloy of the present invention contains 15 to 40% by mass of Ni, 1.5 to 10% by mass of Al, and 30% by mass or less of Co, with the balance being Fe and inevitable impurities. The Fe—Ni—Al- based alloy is subjected to solution treatment at a temperature of 800 ° C. or higher, and then subjected to aging treatment at a temperature of 200 ° C. or higher and lower than 800 ° C.
[0009]
The third Fe-based shape memory alloy of the present invention contains 15 to 40% by mass of Ni and 1.5 to 10% by mass of Al, and further contains 0.001 to 15% by mass of Ti , B or Cr , and the balance. Fe-Ni-Al alloy comprising Fe and unavoidable impurities is solution treated at a temperature of 800 ° C. or higher, and then subjected to aging treatment at a temperature of 200 ° C. or higher and lower than 800 ° C.
[0010]
The fourth Fe-based shape memory alloy of the present invention contains 15 to 40% by mass of Ni, 1.5 to 10% by mass of Al, and 30% by mass or less of Co, and further 0.001 to 15 % by mass of Ta. Alternatively, after Fe-Ni-Al alloy containing 0.001 % by mass to less than 1.5 % by mass of Si and the balance being Fe and inevitable impurities at a temperature of 800 ° C. or higher, 200 ° C. to 800 ° C. It is characterized by being subjected to an aging treatment at a temperature of less than ° C.
[0011]
Any of the first to fourth Fe-based shape memory alloys preferably contains an ordered phase having an fcc and / or fct structure such as Ni 3 Al. This improves the shape memory characteristics.
[0012]
The first Fe-based shape memory alloy production method of the present invention contains 15 to 40% by mass of Ni and 1.5 to 10% by mass of Al, the balance being Fe and Ni—an inevitable impurity. The aluminum alloy is subjected to solution treatment at a temperature of 800 ° C. or higher, and then subjected to aging treatment at a temperature of 200 ° C. or higher and lower than 800 ° C.
[0013]
The production method of the second Fe-based shape memory alloy of the present invention contains 15 to 40% by mass of Ni, 1.5 to 10% by mass of Al, and 30% by mass or less of Co, with the balance being Fe and inevitable. Fe-Ni-Al alloy composed of mechanical impurities is solution treated at a temperature of 800 ° C or higher , and then aging is performed at a temperature of 200 ° C or higher and lower than 800 ° C.
[0014]
The third Fe-based shape manufacturing method of a storage alloys of the present invention, and 15 to 40 wt% Ni, and containing a 1.5 to 10 mass% of Al, further Ti, containing B or Cr 0.001 to 15 wt% The Fe—Ni—Al-based alloy consisting of Fe and inevitable impurities as a balance is subjected to a solution treatment at a temperature of 800 ° C. or higher, and then subjected to an aging treatment at a temperature of 200 ° C. to less than 800 ° C.
[0015]
The method of manufacturing the fourth Fe-based shape memory alloys of the present invention, and 15 to 40 wt% Ni, and contains a 1.5 to 10 wt% of Al, and Co of 30 wt% or less, further 0.001 to 15 mass % of Ta or less than 0.001 mass% or more to 1.5 mass% Si containing from 0.001 wt%, solution treatment Fe-Ni-Al alloy and the balance being Fe and unavoidable impurities at a temperature above 800 ° C. And then aging treatment at a temperature of 200 ° C. to less than 800 ° C.
[0016]
In the first to fourth methods for producing Fe-based shape memory alloys, after solution treatment, an aging treatment is further performed at a temperature of 200 ° C. or higher and lower than 800 ° C. to thereby form an fcc and / or fct structure such as Ni 3 Al. The ordered phase is deposited.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
[1] Composition of Fe-Ni-Al alloys
(a) Basic composition The basic composition of the Fe-Ni-Al alloy constituting the Fe-based shape memory alloy of the present invention contains 15 to 40% by mass of Ni and 1.5 to 10% by mass of Al, and the balance Consists of Fe and inevitable impurities. In the present specification, unless otherwise specified, the content of each element is based on the whole alloy (100% by mass).
[0018]
By containing Ni, the martensitic transformation temperature of the Fe-based shape memory alloy is lowered and the parent phase (fcc phase) is stabilized. When the Ni content is less than 15% by mass, a plate-like martensite structure is not generated. On the other hand, if it exceeds 40% by mass, the martensitic transformation temperature is excessively lowered and no transformation appears in the practical temperature range, so that good shape memory characteristics cannot be obtained. A preferable Ni content is 20 to 38% by mass.
[0019]
By containing Al, an ordered phase having an fcc and / or fct structure such as Ni 3 Al is precipitated by an aging treatment described later. When the Fe-based shape memory alloy contains the ordered phase, the matrix phase is strengthened and the shape memory characteristics are improved. The Al content varies depending on the Ni content, but is preferably 2 to 8% by mass, and more preferably 3 to 8% by mass.
[0020]
(b) Elements other than the basic composition
The Fe—Ni—Al alloy preferably contains a Co element in addition to the above basic composition. By containing Co, the rigidity of the parent phase is lowered and transformation strain is reduced, and as a result, shape memory characteristics are improved. The Co content is preferably 30% by mass or less, and more preferably 0.01 to 15% by mass. If the Co content exceeds 30% by mass, the cold workability of the alloy may be reduced.
[0021]
Fe-Ni-Al-based alloys include Be, Cu, V, Mo, W, Nb, Ti, Zr, Ta, C, B, Cr, Mn, Hf, Re, Y, Ru, Ir, Ga, Si and It can contain at least one selected from the group consisting of Ge. The total content of these elements is preferably 0.001 to 15% by mass, more preferably 0.001 to 12% by mass, and still more preferably 0.001 to 10% by mass. These elements have the effect of increasing the strength of the Fe-based shape memory alloy by refining crystal grains. However, if the total content of these elements exceeds 15% by mass, the alloy may become brittle.
[0022]
By adding Be or Cu, solid solution strengthening occurs, the strength of the parent phase is increased, and the shape memory characteristics are improved. A preferable content of Be and Cu is 1% by mass or less.
[0023]
Ti, Zr, Ta, V, Mo, W, Nb, Hf, Re, Ru, Ir, Ga, Si, and Ge are elements that reduce the product phase defect energy of the parent phase and easily generate a plate-like martensite structure. It is. These elements have the effect of strengthening the matrix phase by precipitating an intermetallic compound phase with Ni. The preferable content of Ti, Zr, Ta, V, Mo, W, Nb, Hf, Re, Ru, Ir, Ga, Si, and Ge is 10% by mass or less. A more preferable content of Si is 0.001% by mass or more and less than 1.5% by mass. A more preferable content of Ti is 0.001% by mass or more and less than 2.5% by mass.
[0024]
By adding B together with Ti, the effect of refining the crystal structure is improved. A preferable content of B is 1% by mass or less.
[0025]
By adding C, the transformation strain of the martensite structure is reduced, the shape memory characteristics are improved and the Ms point is lowered, so that the content of relatively expensive Ni can be reduced. The preferable content of C is 1% by mass or less. Further, by adding C together with Ti, TiC is precipitated, and the effect of refining the crystal structure is improved.
[0026]
Cr and Y are effective elements for maintaining wear resistance and corrosion resistance. A preferable content of Cr and Y is 10% by mass or less.
[0027]
Since Ms point falls by adding Mn, content of relatively expensive Ni can be reduced. The preferable content of Mn is 5% by mass or less.
[0028]
[2] Method for producing Fe-based shape memory alloy
(a) Fe-Ni-Al alloy molding Fe-Ni-Al alloy of the above composition is melt cast, hot working (hot rolling etc.), cold working (cold rolling etc.), press etc. It is formed into a desired shape by processing. The Fe—Ni—Al alloy having the above composition is rich in hot workability and cold workability, and can be easily formed into various shapes such as ultrafine wires and foils.
[0029]
(b) Solution treatment Next, the solution is heated to a solid solution temperature range to transform the crystal structure to austenite (fcc phase) and then rapidly cooled. Solution treatment is performed at a temperature of 800 ° C or higher. The treatment temperature is preferably 900 to 1400 ° C. The holding time at the treatment temperature may be 0.1 minutes or more, but if it exceeds 60 minutes, the effect of oxidation cannot be ignored, so it is preferably 0.1 to 60 minutes. After the heat treatment, a martensite structure is obtained by quenching at a rate of 50 ° C./second or more. When the cooling rate is less than 50 ° C./second, the β phase (B2 structure β phase) is precipitated, and shape memory properties cannot be obtained. A preferable cooling rate is 200 ° C./second or more. The rapid cooling is performed in a refrigerant such as water or by forced air cooling.
[0030]
(c) Aging treatment Although a good shape memory characteristic can be obtained only by solution treatment, by performing the aging treatment, a regular phase having an fcc and / or fct structure such as Ni 3 Al appears, and the matrix phase is strengthened. And shape memory characteristics are improved. The aging treatment is performed at a temperature of 200 ° C or higher and lower than 800 ° C. When the treatment is performed at less than 200 ° C., precipitation of the ordered phase becomes insufficient. On the other hand, when it is processed at 800 ° C. or higher, a β phase which is a stable phase is precipitated.
[0031]
The aging treatment time varies depending on the composition of the Fe-based shape memory alloy and the treatment temperature, but is preferably 1 minute or more, and more preferably 30 minutes to 100 hours. If the aging treatment time is less than 1 minute, the effect is insufficient. On the other hand, if the aging treatment time is unnecessarily prolonged (for example, several hundred hours), the β phase may precipitate and the shape memory property may be lost.
[0032]
[3] Characteristics of Fe-based shape memory alloy The Fe-based shape memory alloy of the present invention has a plate-like martensite structure, and has stable and good shape memory characteristics and superelasticity in a practical temperature range. In particular, the shape recovery rate is approximately 30% or more when aging treatment is performed, and is approximately 50% or more when Co is further contained. Moreover, the yield stress (0.2% proof stress) is approximately 250 MPa or more, and particularly approximately 450 MPa or more when aged. Furthermore, since the Fe-based shape memory alloy of the present invention has good hardness, tensile strength and elongation at break, it is excellent in workability.
[0033]
【Example】
The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
[0034]
Example 1
A Fe-Ni-Al alloy having the composition of samples 1 to 13 shown in Table 1 is melted and solidified at a cooling rate of 140 ° C./min to produce a cylindrical ingot having a diameter of 20 mm and a length of 120 mm. did. This ingot was hot-rolled 4 times at 1200 ° C. and then cold-rolled 10 times to produce a plate material having a thickness of 0.2 mm. Each plate was heat-treated at 1300 ° C. for 10 minutes, then poured into ice water and rapidly cooled (solution treatment). Next, an aging treatment was performed at 600 ° C. to obtain a plate-like sample of Fe-based shape memory alloy. The aging treatment time is as shown in Table 1.
[0035]
[Table 1]
The physical property of each obtained board | plate material was measured with the following method. The measurement results are shown in Tables 2 and 3.
[0037]
(1) Hardness (Vickers hardness)
A micro Vickers hardness tester (MVK-H1 manufactured by Akashi Seisakusho Co., Ltd.) was used.
(2) Shape recovery rate Each plate was wound around a round bar having a diameter of 10 mm in liquid nitrogen, taken out from liquid nitrogen, and the radius of curvature R 0 in a bent state was measured. Next, the bent plate material is heated to 600 ° C., and the radius of curvature R 1 after the shape recovery is measured is measured by the following formula:
Shape recovery rate (%) = 100 × (R 1 −R 0 ) / R 1
Thus, the shape recovery rate was calculated.
(3) Tensile test
In accordance with JIS Z 2241, the tensile strength, elongation at break and yield stress (0.2% yield strength) were determined.
[0038]
[Table 2]
[Table 3]
As can be seen from Tables 2 and 3, all of Samples 1 to 13 exhibited good shape memory characteristics. In particular, Samples 4 to 10 containing the Co element showed a higher shape recovery rate than the plate material not containing Co.
[0041]
Example 2
A Fe—Ni—Al-based alloy having the same composition as Sample 4 shown in Table 1 was formed into a plate material by the same method as in Example 1, solution treated (quenched) under the same conditions as in Example 1, and then 0 ° C. at 600 ° C. Each aging treatment was performed for 4 hours, 13 hours, 36 hours and 100 hours. The shape recovery rate and Vickers hardness of each obtained plate were measured by the same method as in Example 1. The results are shown in FIG. As can be seen from FIG. 2, the shape recovery rate of the solution material (quenching) alone is less than 10% and the Vickers hardness is low, but as the aging treatment time becomes longer, both the shape recovery rate and the Vickers hardness are remarkably increased. Improved. Further, when the plate material which had been subjected to aging treatment for 36 hours was observed with a transmission electron microscope (see FIG. 3, 160,000 times), it was found that a fine fcc ordered phase having a diameter of several nm was precipitated.
[0042]
【The invention's effect】
As described in detail above, the Fe-based shape memory alloy of the present invention has stable and good shape memory characteristics in a practical temperature range. Furthermore, since the Fe-based shape memory alloy of the present invention is composed of an Fe-Ni-Al alloy, the material cost is low and the workability and corrosion resistance are excellent. Can be manufactured.
[Brief description of the drawings]
1 is an optical micrograph showing a plate-like martensitic structure of an Fe-based shape memory alloy plate material of Sample 5 of Example 1. FIG.
2 is a graph showing the relationship between aging treatment time, shape recovery rate, and Vickers hardness in Example 2. FIG.
3 is a transmission electron micrograph of an Fe-based shape memory alloy sheet material that was subjected to aging treatment for 36 hours in Example 2. FIG.
Claims (9)
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| US7300708B2 (en) * | 2004-03-16 | 2007-11-27 | General Electric Company | Erosion and wear resistant protective structures for turbine engine components |
| WO2007055155A1 (en) | 2005-11-09 | 2007-05-18 | Japan Science And Technology Agency | Iron-based alloy having shape-memory property and superelasticity and method for manufacture thereof |
| CN101674861B (en) | 2007-05-09 | 2012-07-04 | 独立行政法人科学技术振兴机构 | Guide wire and stent |
| WO2011046055A1 (en) | 2009-10-14 | 2011-04-21 | 独立行政法人科学技術振興機構 | Ferrous shape memory alloy and production method therefor |
| JP5929251B2 (en) * | 2012-01-31 | 2016-06-01 | 株式会社豊田中央研究所 | Iron alloy |
| CN103233159B (en) * | 2013-04-07 | 2015-06-17 | 南昌大学 | Polycrystalline Fe-based shape-memory hyperelastic alloy and preparation method thereof |
| JP6874246B2 (en) | 2016-09-06 | 2021-05-19 | 国立大学法人東北大学 | Fe group shape memory alloy material and its manufacturing method |
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| CN111041387B (en) * | 2019-12-25 | 2020-10-27 | 南京龙浩新材料科技有限公司 | Multi-element iron-based shape memory alloy and preparation method thereof |
| CN113564441A (en) * | 2021-07-19 | 2021-10-29 | 哈尔滨工程大学 | Fe-Ni-Co-Al-W alloy with super elasticity and preparation method thereof |
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