Effects of phase transformation on the microstructures and magnetostriction of Fe-Ga and Fe-Ga-Zn ferromagnetic shape memory alloys

Abstract

The phase transformation and magnetostriction of bulk Fe 73 Ga 27 and Fe 73 Ga 18 Zn 9 (at. %) ferromagnetic shape memory alloys (FSMs) were investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD), and a magnetostrictive-meter setup. For the Fe 73 Ga 27 FSM alloy solution treated at 1100 C for 4 h and quenched in ice brine, the antiphase boundary segments of the D0 3 domain were observed in the A2 (disordered) matrix, and the Fe 73 Ga 27 FSM alloy had an optimal magnetostriction (k k s ¼ 71 Â 10 À6 and k ? s ¼ À31 Â 10 À6 ). In Fe 73 Ga 27 FSM alloy as-quenched, aged at 700 C for 24 h, and furnace cooled, D0 3 nanoclusters underwent phase transformation to an intermediate tetragonal phase (i.e., L1 0 -like martensite) via Bain distortion, and finally L1 2 (Fe 3 Ga) structures precipitated, as observed by TEM and XRD. The L1 0 -like martensite and L1 2 phases in the aged Fe 73 Ga 27 FSM alloy drastically decreased the magnetostriction from positive to negative (k k s ¼ À20 Â 10 À6 and k ? s ¼ À8 Â 10 À6 ). However, in Fe 73 Ga 18 Zn 9 FSM alloy as-quenched and aged, the phase transformation of D0 3 to an intermediate tetragonal martensite phase and precipitation of L1 2 structures were not found. The results indicate that the aged Fe 73 Ga 18 Zn 9 FSM alloy maintained stable magnetostriction (k k s ¼ 36 Â 10 À6 and k ? s ¼ À31 Â 10 À6 ). Adding Zn can improve the ferromagnetic shape memory effect of aged Fe 73 Ga 18 Zn 9 alloy, which may be useful in application of the alloy in high temperature environments. V C 2015 AIP Publishing LLC. [http://dx.The Fe-Ga (Galfenol) FSM alloy systems have received much attention because they exhibit both magnetic field induced strain and the magnetic shape memory effect. In addition, Fe-Ga alloys have high saturation magnetostriction in low applied magnetic fields, so the alloys have a potential application in magnetostrictive actuators and sensors. For bulk polycrystalline multiphase Fe-Ga alloys, A2, D0 3 , and L1 2 structures have been reported to coexist in rapidly quenched alloys 1 as well as in mechanically alloyed systems. 2 In the case of arc-melted alloys, a mixture of only two phases (A2 and D0 3 -type) has been observed. 3-5 From the above review, it is clear that the degree of ordering is likely to be very sensitive to the details of alloy production. 6,7 In this work, TEM study confirms that in Fe 73 Ga 27 FSM alloy solution-treated at 1100 C for 4 h and quenched in ice brine (as-quenched), antiphase boundary segment (APBs) of the D0 3 domain were present in the A2 matrix. When the Fe 73 Ga 27 FSM alloy was as-quenched and aged at 700 C for 24 h (as-quenched and aged), the D0 3 nanoclusters underwent phase transformation to an intermediate tetragonal phase (L1 0 -like martensite) via Bain distortion, and finally L1 2 structures precipitated, as demonstrated by TEM and XRD analyses. The L1 0 -like martensite and L1 2 structures in the aged Fe 73 Ga 27 FSM alloy drastically decreased the magnetostriction from positive to negative, as also confi...

Anelasticity of Phase Transitions and Magnetostriction in Fe-(27-28%)Ga Alloys

“…Anelastic effects for phase transitions at higher temperatures have as yet not been reported in the literature. Doping Fe-Ga with rare earth elements enhances magnetostriction in Fe- (17)(18)(19)Ga alloys by creating local inhomogeneities [9][10][11] and stabilizes the metastable bcc-derivative phase in as cast Fe-27Ga alloys by preventing L1 2 phase nucleation on the D0 3 grain boundaries 7,[12][13][14] . The structure of metastable Fe-27Ga type alloys before their transition to equilibrium L1 2 phase may show several metastable phases (A2, B2, D0 3 ), the size of which, as reported in the literature, can be from nano (e.g.…”

Influence of Dy substitution for Ga on the magnetic properties of arc-melted Fe-Ga alloys

“…The Dy content seems to blend with the Fe-Ga alloys, which improves the microstructural properties [30]. The existence of D0 3 and L1 2 phases along with the A2 phase is confirmed by the excess of grain size.…”

Progress on improvement and application of magnetostrictive properties of the Fe-Ga alloy

“…Gao et al [19] found that adding Cr to polycrystalline Fe-Ga alloy can significantly improve the mechanical properties at room temperature, while the magnetostrictive coefficient is only 70ppm. If Fe73Ga18Zn9 is prepared by adding 9% Zn into fe73ga27 alloy, after quenching and aging at 700 ℃ for 24 hours, it can improve the magnetostrictive property and maintain stability, and improve the ferromagnetic shape memory effect, which provides the possibility for the application of the alloy in high-temperature environment [20].…”