Shape memory alloys have made rapid progress in many domains, primarily biomedical (endovascular stents, orthodontic archwires), and engineering (smart actuators, robotics, hydraulic couplings). The selection of a shape memory alloy for the indented application is based on its characteristic phase transformation temperatures. These characteristic temperatures are influenced by myriad parameters, such as composition, microstructure of the alloy, defect density, etc. When an shape memory alloy under an external load is subjected to cyclic operations to perform useful work, for example, actuators, these characteristic temperatures are modified. This study, therefore, aims to understand the influence of external loading on the shape memory characteristics of a Ni50Ti45Cu5 (at.%) alloy. A wire of 1.43 mm diameter and length of 100 mm was subjected to heating and cooling between its phase transformation temperatures in a cyclic manner under constant stress (of up to 60 MPa). The maximum recovery strain, actuation/retraction rate, and the stress influence coefficient were determined and compared with those of the other Ni-Ti and Cu-based shape memory alloys. The results show that raising the load level causes an increase in the transition temperatures, especially the Ms (martensite start temperature) rather than the other phase transformation temperatures (martensite finish (Mf), austenite start (As), austenite finish (Af)). It also significantly affects the recovery strain and the rate of retraction during forward transformation and the symmetry of operation.

中文翻译：

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施加应力对热机械循环 Ni50Ti45Cu5 (at.%) 合金形状记忆特性的影响

形状记忆合金在许多领域取得了快速进展，主要是生物医学（血管内支架、正畸弓丝）和工程（智能执行器、机器人、液压联轴器）。针对凹痕应用选择形状记忆合金是基于其特征相变温度。这些特征温度受到无数参数的影响，例如合金的成分、微观结构、缺陷密度等。当形状记忆合金在外部负载下进行循环操作以执行有用功时，例如执行器，这些特征温度被修改。因此，本研究旨在了解外部载荷对镍形状记忆特性的影响50钛45铜5(at.%) 合金。将直径为 1.43 mm、长度为 100 mm 的线材在恒定应力（高达 60 MPa）下以循环方式在其相变温度之间进行加热和冷却。确定了最大恢复应变、驱动/回缩率和应力影响系数，并与其他镍钛和铜基形状记忆合金进行了比较。结果表明，提高负载水平会导致转变温度升高，尤其是 Ms（马氏体开始温度）而不是其他相变温度（马氏体结束温度（MF), 奥氏体开始 (As), 奥氏体表面处理 (AF））。它还显着影响正向变换过程中的恢复应变和回缩率以及操作的对称性。