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

The phase transformation and magnetostriction of bulk Fe73Ga27 and Fe73Ga18Zn9 (at.%) ferromagnetic shape memory alloys (FSMs) were investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD), and a magnetostrictive-meter setup. For the Fe73Ga27 FSM alloy solution treated at 1100 degrees C for 4 h and quenched in ice brine, the antiphase boundary segments of the D(0)3 domain were observed in the A2 (disordered) matrix, and the Fe73Ga27 FSM alloy had an optimal magnetostriction (lambda(s)(parallel to) = 71 x 10(-6) and lambda(s)(perpendicular to) = 31 x 10(-6)). In Fe73Ga27 FSM alloy as-quenched, aged at 700 degrees 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) (Fe3Ga) structures precipitated, as observed by TEM and XRD. The L1(0)-like martensite and L1(2) phases in the aged Fe73Ga27 FSM alloy drastically decreased the magnetostriction from positive to negative (lambda(s)(parallel to) = 20 x 10(-6) and lambda(s)(perpendicular to) = 8 x 10(-6)). However, in Fe73Ga18Zn9 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 Fe73Ga18Zn9 FSM alloy maintained stable magnetostriction (lambda(s)(parallel to) = 36 x 10(-6) and lambda(s)(perpendicular to) = 31 x 10(-6)). Adding Zn can improve the ferromagnetic shape memory effect of aged Fe73Ga18Zn9 alloy, which may be useful in application of the alloy in high temperature environments. (C) 2015 AIP Publishing LLC.