Novel Research for Development of Shape Memory Alloys

Shape memory alloys have attracted much attention due to their attractive properties for applications as well as their basic aspects of deformation and transformation in structural and magnetic behavior. In 1951, the Au–Cd alloy was discovered [1]. After that, numberless shape memory alloys have been developed. A lot of applications of shape memory alloys were realized after the Ti–Ni alloy was found in 1963 and developed extensively in 1980s [2]. Recently, ferromagnetic shape memory alloys (FSMA) have been studied as candidates for highly functional materials [3]. Among FSMA, Ni2MnGa is the most renowned [4]. The magnetostriction, or magnetic field induced strain (MFIS) is most featured phenomena. Few % MFIS were found for some Ni2MnGa type single crystals. MFISs of 6.0% have been produced at room temperature in single crystals of Ni49.8Mn28.5Ga21.7 (TM = 318 K) by application of fields of order 400 kA/m (=0.50 T) under an opposing stress of order 1 MPa [5]. Fe–Pd and Fe–Pt alloys are also famous FSMA for MFIS. The strain is the result of field-induced twin boundary motion under an atmospheric pressure. A disordered Fe-31.2%Pd (at %) alloy (A1-type cubic) [6,7], and an ordered Fe3Pt (L12-type cubic) ferromagnetic alloy [8,9], have attracted much interest due to the large MFISs. The alloys which was doped other elements are also studied. The magnetostriction studies on the premartensite phase of related Cr-substituted Ni2Mn1−xCrxGa alloys were studied and robust 120 ppm magnetostriction was observed [10]. New alloys in the Ni–Mn–In, Ni–Mn–Sn, and Ni–Mn–Sb Heusler alloy systems that are expected to be ferromagnetic shape memory alloys have been studied [11]. A re-entrant magnetism was observed in some alloys [12,13]. These alloys are promising as a metamagnetic shape memory alloys with a magnetic field-induced shape memory effect and as magnetocaloric effect [14]. Consequently, these materials are finding use or are candidates as materials for sensors, actuators, magnetic refrigerator, etc. [15]. The dynamical functionality of the nickel–titanium (NiTi)-based alloy comes into the limelight. NiTi is an attractive alloy due to its unique functional properties, for example, shape memory effect (SMA), elastic deformation, super-elasticity, low stiffness, and damping characteristics [16,17]. In this special issue, physical properties are also shown for industrial objects, as joining between the different kind of metals, SMA bolts, and tubes. In our department in Ryukoku Univertsity, we are focused on robotics and applications (mechanical actuators). Therefore, our colleagues shed light on dynamic applications for SMAs.