【発明の詳細な説明】[Detailed description of the invention]
本発明はCu―Zn―Al系形状記憶合金の改良に
関するもので、特に形状記憶効果を損なうことな
く冷間加工と強度を向上せしめたものである。
一般に形状記憶合金は、マルテンサイト変態温
度以上の領域で所定形状に成形し、これをマルテ
ンサイト変態温度以下の領域で変形した後、マル
テンサイト変態温度以上に加熱すると所定形状に
回復し、またマルテンサイト変態温度近傍におい
て超弾性を示すもので、種々の合金が開発され、
形状記憶効果や超弾性を利用して種々の用途に用
いられている。このような形状記憶合金中、Cu
―Zn―Al系形状記憶合金は価格的に有利なため
各種用途への適用が検討され、用途によつては実
用化されている。
従来Cu―Zn―Al系形状記憶合金は熱間加工
後、高温域（β相）で加熱処理してから、冷間加
工を行なつているが、加熱処理中に結晶粒が粗大
化し易く、場合によつては結晶粒が１〜３mmにも
粗大化し、冷間加工性を著しく損なう欠点があつ
た。また結晶粒の粗大化は二方向性形状記憶効果
の利用において、繰返し使用回数（寿命）を短縮
し、超弾性の利用においても、もともと弾性異方
性が大きいことから、負荷応力方向の非選択性に
つながる欠点があつた。
本発明はこれに鑑み種々検討の結果、Cu―Zn
―Al系形状記憶合金に、Crを微量添加すること
により、形状記憶効果を損なうことなく、結晶粒
を微細化し、加熱処理による結晶粒の粗大化を抑
制し得ることを知見し、更に検討の結果冷間加工
性の良好なCu―Zn―Al系形状記憶合金を開発し
たものである。
即ち本発明形状記憶合金は、Al 0.05〜10.0wt
％（以下wt％を単に％と略記）、Zn9.0〜40.0％、
Cr0.1〜0.4％を含み、残部Cuからなることを特
徴とするものである。
しかして本発明において、合金組成を上記の如
く限定したのは次の理由によるものである。
Al及びZnは形状記憶効果を得るために添加す
るもので、Al含有量を0.05〜10.0％、Zn含有量を
9.0〜40.0％と限定したのは、Al含有量が0.05％
未満でも、Zn含有量が9.0％未満でも必要とする
マルテンサイト変態温度が低くなりすぎるばかり
か、形状記憶効果が得られない場合もあり、Al
含有量が10.0％を越えても、Zn含有量が40.0％を
越えてもγ相が析出し、冷間加工性が悪化するば
かりか、形状記憶効果が得られない場合もあるた
めである。
Crを添加するのは、合金の形状記憶効果を損
なうことなく結晶粒を微細化し、加熱処理におけ
る結晶粒の粗大化を抑制して冷間加工性の向上を
図つたもので、その含有量を0.1〜0.4％と限定し
たのは0.1％未満では結晶粒の微細化が不十分で
あり、0.4％を越えると結晶粒は微細化するも形
状記憶効果が損なわれるためである。
以下本発明合金を実施例について詳細に説明す
る。
黒鉛ルツボを用いてCuを溶解し、その湯面を
木炭粉末で覆い、これにCr、Zn、Alを順次添加
して第１表に示す組成の合金を溶製し、これを鋳
造して長さ180mmのインチバーと幅150mm、厚さ25
mm、長さ200mmの鋳塊を得た。
この鋳塊表面をそれぞれ一面あたり2.5mm面削
した後、熱間圧延により直径８mmの棒と幅150
mm、厚さ８mmの板を作成し、これを600〜700℃の
温度に加熱焼鈍した後、棒について伸線加工を行
ない、板について冷間圧延を行なつて冷間加工性
を調べ、冷間加工材について強度及び形状記憶特
性を測定した。これ等の結果を第１表に併記し
た。
第１表中冷間加工性は加工率80％で表面にササ
クレや割れが発生しないものを〇印、加工率70％
では表面にササクレや割れを発生せず、80％で表
面にササクレや割れをわずかに発生するものを△
印、加工率80％で断線や割れ破壊を発生するもの
を×印で示した。
また引張強さは加工率60％の冷間加工材につい
て、JIS Z2241に基いて測定した。
また形状記憶特性は、直径1.0mmの伸線加工材
を用い、マルテンサイト変態温度以上で直径10
mm、長さ50mmのコイルを作成し、これをマルテン
サイト変態終了温度より30℃低い温度でコイルを
長さ100mmに引き伸ばし、これをマルテンサイト
逆変態終了温度より30℃高い温度に加熱したと
き、完全にもとの長さ（50mm）に縮むものを〇
印、完全にもとの長さに縮まらないものを×印で
示した。
The present invention relates to the improvement of Cu--Zn--Al type shape memory alloys, and in particular improves cold working and strength without impairing the shape memory effect. In general, shape memory alloys are formed into a predetermined shape in a region above the martensitic transformation temperature, deformed in a region below the martensitic transformation temperature, and then recovered to the desired shape when heated above the martensitic transformation temperature. It exhibits superelasticity near the site transformation temperature, and various alloys have been developed.
It is used for various purposes by taking advantage of its shape memory effect and superelasticity. In such shape memory alloys, Cu
-Zn-Al-based shape memory alloys are economically advantageous, so their application to various applications has been considered, and in some applications they have been put into practical use. Conventionally, Cu-Zn-Al shape memory alloys are heat-treated in a high temperature range (β phase) after hot working, and then cold-worked, but the crystal grains tend to coarsen during the heat treatment. In some cases, the crystal grains became as coarse as 1 to 3 mm, resulting in a drawback that the cold workability was significantly impaired. In addition, coarsening of crystal grains shortens the number of repeated uses (life) when using the bidirectional shape memory effect, and when using superelasticity, since elastic anisotropy is originally large, the direction of applied stress cannot be selected. I had a flaw connected to my sexuality. In view of this, the present invention was developed as a result of various studies.
- It was discovered that by adding a small amount of Cr to an Al-based shape memory alloy, it was possible to refine the crystal grains and suppress the coarsening of the crystal grains due to heat treatment without impairing the shape memory effect. As a result, a Cu-Zn-Al shape memory alloy with good cold workability was developed. That is, the shape memory alloy of the present invention contains Al 0.05 to 10.0wt
% (hereinafter wt% is simply abbreviated as %), Zn9.0~40.0%,
It is characterized by containing 0.1 to 0.4% Cr, with the remainder being Cu. However, in the present invention, the alloy composition is limited as described above for the following reasons. Al and Zn are added to obtain a shape memory effect, and the Al content is 0.05 to 10.0% and the Zn content is
The Al content is limited to 9.0 to 40.0% when the Al content is 0.05%.
Even if the Zn content is less than 9.0%, the required martensitic transformation temperature will not only be too low, but also the shape memory effect may not be obtained.
This is because even if the Zn content exceeds 10.0% or even if the Zn content exceeds 40.0%, the γ phase will precipitate, which will not only deteriorate cold workability but also prevent the shape memory effect from being obtained. The purpose of adding Cr is to refine the crystal grains without impairing the shape memory effect of the alloy, suppress coarsening of the crystal grains during heat treatment, and improve cold workability. The reason why it is limited to 0.1 to 0.4% is that if it is less than 0.1%, the crystal grains will not be refined enough, and if it exceeds 0.4%, although the crystal grains will be refined, the shape memory effect will be impaired. EXAMPLES The alloy of the present invention will be described in detail below with reference to Examples. Cu is melted using a graphite crucible, the surface of the melt is covered with charcoal powder, Cr, Zn, and Al are sequentially added to the melt to produce an alloy having the composition shown in Table 1, which is then cast into a long piece. Inch bar length 180mm and width 150mm, thickness 25
An ingot with a length of 200 mm was obtained. After each surface of this ingot was milled 2.5mm per side, it was hot rolled into a bar with a diameter of 8mm and a width of 150 mm.
After preparing a plate with a thickness of 8 mm and annealing it at a temperature of 600 to 700°C, the rod was wire-drawn, the plate was cold-rolled, and the cold workability was examined. The strength and shape memory properties of the pre-processed materials were measured. These results are also listed in Table 1. In Table 1, cold workability is marked with ○ if no cracking or cracking occurs on the surface at a processing rate of 80%, and a processing rate of 70%.
△: No cracks or cracks on the surface, but 80% with slight cracks or cracks on the surface.
The marks indicate wire breaks and cracks that occur at a processing rate of 80%. In addition, the tensile strength was measured based on JIS Z2241 for cold-worked materials with a working rate of 60%. In addition, the shape memory property was determined by using a wire-drawn material with a diameter of 1.0 mm and a diameter of 10 mm at a temperature above the martensitic transformation temperature.
When you create a coil with a length of 50 mm and stretch it to a length of 100 mm at a temperature 30°C lower than the martensitic transformation end temperature, and then heat it to a temperature 30°C higher than the martensitic reverse transformation end temperature, Items that completely shrink to their original length (50 mm) are marked with an ○, and items that do not completely shrink to their original length are marked with an x.
【表】
第１表から明らかなように、Cu―Zn―Al形状
記憶合金にCrを添加した本発明合金は、良好な
冷間加工性と形状記憶特性を示し、引張強さ87〜
105Kg／mm2の性能を有し、従来合金No.５と比較し
同等のAl及びZn含有量であれば、はるかに優れ
た冷間加工性が得られることが判る。これに対し
Cr含有量が少ない比較合金No.３では冷間加工性
が悪く、Cr含有量の多い比較合金No.４では形状
記憶特性が得られない。
このように本発明合金によれば、優れた冷間加
工性と強度を有し、かつ十分な形状記憶特性を示
すもので、二方向性形状記憶効果の利用において
繰返し利用回数（寿命）を高め、超弾性の利用に
おいて弾性異方性の影響を十分小さくすることが
できる等工業上顕著な効果を奏するものである。[Table] As is clear from Table 1, the alloy of the present invention, which is a Cu-Zn-Al shape memory alloy with Cr added, exhibits good cold workability and shape memory properties, and has a tensile strength of 87~
It has a performance of 105 Kg/mm 2 and compared to conventional alloy No. 5, it can be seen that with the same Al and Zn contents, far superior cold workability can be obtained. In contrast to this
Comparative alloy No. 3, which has a low Cr content, has poor cold workability, and comparative alloy No. 4, which has a high Cr content, does not have shape memory properties. As described above, the alloy of the present invention has excellent cold workability and strength, and also exhibits sufficient shape memory properties, increasing the number of repeated uses (life) when utilizing the bidirectional shape memory effect. , it is possible to sufficiently reduce the influence of elastic anisotropy in the use of superelasticity, and has a remarkable effect industrially.