Phase Equilibria and Phase Transition of the Ni–Fe–Ga Ferromagnetic Shape Memory Alloy System

Abstract

KATSUNARI OIKAWA, TOSHIHIRO OMORI, YUJI SUTOU, HARUHIKO MORITO, RYOSUKE KAINUMA, and KIYOHITO ISHIDA Phase equilibria and martensitic and magnetic transitions of the b (B2 and L2 1 ) phase in the Ni-Fe-Ga system were investigated. The b phase was found to be in equilibrium with the g (A1 structure) or g9 (L1 2 structure) phase. The Curie temperature, T C , equilibrium temperature, T 0 5 (M s 1 A f )/2, martensitic transition starting temperature, M s , and reverse transition finishing temperature, A f , of the b single-phase alloys were sensitive to the Fe and Ga compositions. The Fe substitution for Ni decreased and increased the T 0 and T C , respectively. The Ga substitution for Ni or Fe decreased both the T 0 and T C . The entropy change accompanying the reverse martensitic transition showed compositional dependence due to the magnetic contribution. The saturation magnetization I s of the Ni-Fe-Ga system showed a strong dependence on the magnetic valence Z m . The I s values of the Ni-Fe-Ga alloys annealed at 1023 K showed the same Z m dependence as other ferromagnetic shape memory alloy (FSMA) systems. the two-phase samples was determined by energy-dispersive X-ray spectroscopy using a standard calibration method.

Long-Range Atomic Order and Entropy Change at the Martensitic Transformation in a Ni-Mn-In-Co Metamagnetic Shape Memory Alloy

“…This behavior agrees with the phenomenological model based on a Bragg-Williams approximation recently proposed to describe the evolution of the magnetic contribution to the total entropy change in Ni-Mn-based alloys [34] (a similar behavior has been also reported in Ni-Fe-Ga ferromagnetic shape memory alloys [35]). The absence of a marked change in the slope (previously reported) seems to be due to the paramagnetic nature of martensite in the present Ni-Mn-In-Co alloy.…”

Effects of rotation speed on microstructure and transition temperatures in Ni–Fe–Al melt-spun ribbons

“…Although the rapidly solidified ribbons are reported to show higher T M than annealed ribbons, it can be seen that T 0 has almost linear dependence to the e/a with nearly the same slope for each Al content. This feature is very similar to the above FSMAs [14]. Oikawa et al also showed that the saturation magnetization value, measured at low temperature T ¼ 83 K and at high magnetic field 7 T, had linear dependence with the magnetic valence Z m .…”

“…All of the above FSMAs obey almost the same Z m dependence. The Curie temperature T C also has linear dependence with the Z m [14]. Fig.…”

“…Oikawa et al reported detailed research on the compositional dependence of the martensitic transformation and magnetic properties of CoeNieGa, CoeNieAl, NieFeeGa and NieFeeAl FSMA systems [14]. These systems have similar phase diagrams to the NieFeeAl, compositional region where both ferromagnetism and the martensitic transformation are observed, lies in the vicinity of b/b þ g boundary.…”

“…One of the disadvantages of NieFeeAl FSMA is its low Curie temperatures, T C < 250 K [9]. Reducing Al content is expected to increase both T C and T M of NieFeeAl b alloys [9,14], however the chemical composition of single b phase alloys with Al content less than 25 at.% is restricted by the b/b þ g(g 0 ) solubility boundary [15].…”