Continuously cast shape memory and super elastic alloy wires produced by a new continuous casting route

本研究的目的是开发软铜形状记忆超弹性合金材料，以取代常用的硬Ti-Ni合金。具有高橡胶弹性的铜合金丝有可能成为工业材料中有用的弹簧件。本研究探讨了将OCC工艺应用于Cu-Al-Ni和Cu-Sn形状记忆超弹性合金丝的可能性。确定了用OCC工艺可以连续铸造直径为2mm的形状记忆丝。铸态OCC丝为单晶或单向凝固组织，基体相为β_1， γ_2颗粒沿亚晶界以枝晶形式析出。随着铸造速度的增加，γ_2颗粒越来越少，尺寸越来越细。Cu-Al-Ni合金和Cu-Sn合金的Ms转变温度分别为-19℃~ 3℃和-55℃~ -50℃，在室温下产生超弹性行为。在加热至90℃时，较慢速度铸造的线材表现出形状记忆特性，而在室温下，较高铸造速度铸造的线材表现出超弹性。在较高的铸造速度下生产的Cu-Al-Ni合金丝表现出两步超弹性转变为单晶丝。此外，Cu-Al-Ni合金线材在25000次弯曲循环后发生疲劳失效，是传统Ti-Ni线材的10倍。OCC Cu-Al-Ni合金丝的弯曲性能，如柔软度和疲劳极限，都优于传统的Ti-Ni丝。这些发现表明，OCC工艺可用于生产超弹性单晶或单向凝固铜合金丝。

The aim of this research is development of soft copper shape-memory, super-elastic alloy material in place of the usual hard Ti-Ni alloy. The copper alloy wire with high rubber elasticity has the possibility to become the useful spring part for the industrial materials.In this research, the possibility of applying the OCC process to the fabrication of Cu-Al-Ni and Cu-Sn shape memory, super-elastic alloy wires was investigated. It was established that shape memory wires 2 mm in diameter can be continuously cast by OCC process. Cast OCC wires were found to be of single crystal or unidirectional solidified structure with a matrix phase β_1 in which γ_2 particles were precipitated in the form dendrites along the sub-grain boundaries. The γ_2 particles became fewer and the size became finer with an increase in casting speed. The Ms transformation temperature for the Cu-Al-Ni alloy and Cu-Sn alloy was in the range -19℃ to 3℃ and -55℃ to -50℃, respectively, giving rise to super-elastic behavior at the room temperature. The wires cast at slower speeds displayed shape memory attributes on heating to 90℃, whereas the wires produced at higher casting speeds exhibited super elasticity at room temperature. The Cu-Al-Ni alloy wires produced at higher casting speeds exhibited two-step super-elastic transformations as a single crystal wires. In addition, the fatigue failure of the Cu-Al-Ni alloy wires occurred after 25000 bend cycles, which was 10 times that of the conventional Ti-Ni wires. Bending properties of the OCC Cu-Al-Ni alloy wires, such as the softness and the fatigue limit, were superior to those of the conventional Ti-Ni wires.These findings suggest that the OCC process could be useful for the production of super-elastic single crystal or unidirectional solidified Cu alloy wires.