Martensitic transformation and magnetic properties of Ti-doped NiCoMnSn shape memory alloy

Martensitic transformation, microstructure, and magnetic properties of Ti-doped Ni43-x Ti (x) Co7Mn43Sn7 (at%) (x = 0, 0.5, 1.0, 2.0, and 4.0) shape memory alloys were investigated. The results show that transformation temperatures of Ni43Co7Mn43Sn7 can be efficiently adjusted by the substitution of Ti for Ni. For example, the martensitic transformation starting temperature (M (s)) is reduced by about 278 K with 4 at% addition of Ti. Room temperature microstructure evolves from single tetragonal martensite for the Ti-free alloy to dual phases (tetragonal martensite + second phase) with 0.5 at%, 1.0 at%, and 2.0 at% addition of Ti to dual phases (cubic austenite + second phase) for 4.0 at% Ti-doped alloy. The mechanical properties can be obviously improved by adding an appropriate amount of Ti. A noteworthy point is that magnetic-field-induced reverse transformation is observed in Ni39Ti4Co7Mn43Sn7 alloy.