مقاله انگلیسی رایگان در مورد روش های ساخت آلیاژهای حافظه دار – الزویر 2018

Shape memory alloys (SMAs) are an exquisite class of active materials with an ability to regain its original shape at high temperatures. There is a wide range of alloys which exhibit the shape memory effect, but only those alloys are commercially attractive which show a substantial amount of strain recovery and generate significant force due to shape change. Among the Cu-based shape memory alloys, Cu-Al-Ni alloys have a higher thermal stability than Cu-Zn-Al alloys [1, 2]. Therefore, Cu-Al-Ni alloys are being developed for high temperature applications due to their potential to be used as sensors and actuators at temperatures around 200 ºC. On the other hand, Cu-Zn-Al alloys have maximum working temperatures of 120 °C, but they sh ow better ductility as compared to Cu-Al-Ni alloys for low temperature applications [2]. Shape Memory Effect (SME) is shown by alloys exhibiting crystallographically reversible thermo-elastic martensitic transformation. At a higher temperature, the same alloys have another unique property called as super-elasticity [3]. Superelasticity is caused due to large non-linear recoverable strain (up to 18%) upon loading and unloading, in which a specimen once deformed by application of force regain its original shape automatically without any application of heat [1]. The Ni-Ti, ferrous alloys and Cu-based alloys are considered as practical materials for applications among many shape memory alloys. Ni-Ti alloys, an equi-atomic compound of Ni and Ti, are the most widely used shape memory alloys. They show excellent shape memory strain up to 8 % and are thermally stable. However, the reactivity of Ti limits their processing in air and hence all melting operations are to be carried out in vacuum. In recent decades, Cu-based shape memory alloys have emerged as a potential material for variety of applications, such as high damping material, sensors and actuators. Cu-Al-Ni shape memory alloys have gained special attention due to their high thermal stability among the other Cubased shape memory alloys. The presence of SME, thermo-elastic martensitic transformation and crystallography in the Cu-Al-Ni alloy was confirmed by Otsuka [4-6]. Some ferrous alloys also exhibit SME under certain conditions [7]. Fe-Mn-Si alloys are the most important iron-based shape memory alloy. However, they can recover shape memory strain less than 4 %.