M. Ohtsuka, S. Yamauchi, T. Takagi, K. Itagaki, Tohoku University, Sendai, Japan; M. Matsumoto, Tohoku Gakuin University, Tagajo, Japan
Ni2MnGa alloy is an intelligent material with ferromagnetic and shape memory properties. The application of the alloy films as an actuator of micro-machines has been proposed. Therefore, the mechanical properties of the films are very important in the practical use. In the present study, effects of temperature and magnetic field (MF) on mechanical properties of the films have been investigated. The Ni-rich Ni2MnGa (Ni54Mn23Ga23) films were deposited on a poly-vinyl alcohol substrate with a radio-frequency magnetron sputtering apparatus. After separating from the substrate, the films were heat-treated at 1073K for 3.6ks and cut into 4mm×15mm as the tensile test specimens. The martensitic transformation temperatures (Ms = 324K, Mf = 313K, As = 316K and Af = 339K) were higher than RT and lower than the Curie temperature (TC = 356K). The tensile test (nominal strain rate: 2×10-5s-1) was performed at 273~373K under 0~1T. The MF was applied parallel to the tensile axis. The specimen was deformed up to 1% strain by repeating the cycle of loading and unloading while gradually increasing by 0.25% strain. The plastic deformation starting stress (σp) and effective elastic modulus (Eeff) were defined from the stress-strain curves. σp in the austenitic (A) phase (above Af) was larger than that in the martensitic (M) phase (below As) and the (M+A) two phases (between As and Af). Eeff of A phase was slightly larger than that of M phase and (M+A) phases. σp decreased by applied MF below As or between As and Af, while Eeff slightly increased.
Summary: The effects of temperature and magnetic field on mechanical properties of the ferromagnetic shape memory alloy Ni
2MnGa sputtered films have been investigated. The plastic deformation starting stress (σ
p) and effective elastic modulus (
Eeff) were defined to evaluate the mechanical properties of the films qualitatively from the stress-strain curves.
