Novel Co-Al-Si Shape Memory Alloys with B2-Structured Parent Phase

Shape memory alloys, such as Ti-Ni-based (Ti-Ni, Ti-Ni-Cu), Cu-based (Cu-Al-Ni, Cu-Zn-Al), and Fe-based (Fe-Ni-Co-Al-Ta-B, Fe-Mn-Al-Ni) alloys, display shape memory effect and pseudoelasticity due to thermoelastic martensitic transformation. They have offered many technology advantages for various applications such as eyeglass frames, coupling devices, medical devices, and seismic dampers. In recent years, some Co-based shape memory alloys such as Co-Ni-Ga have been reported and they have attracted much attention because of their ability to be used at high temperatures above 373 K. In this study, we present the results of novel Co-Al-Si shape memory alloys showing the thermoelastic martensitic transformation from a B2-structured parent phase. The crystal structures of parent and martensite phases were determined by transmission electron microscopy (TEM), and the transformation temperatures were investigated by measuring the temperature dependence of electric resistivity. Furthermore, it was found that some alloys show excellent pseudoelasticity at temperatures from 298 K to 453 K. Thus, the new Co-based shape memory alloys show great promise for applications requiring high-temperature pseudoelastic properties.