Microstructures and magnetostrictive strains of Fe-Ga-Ni ferromagnetic shape memory alloys

Abstract

Transmission electron microscopy (TEM), a magnetostrictive-meter setup, and a superconducting quantum interference device magnetometer were used to investigate the microstructures, saturation magnetostriction, and magnetic properties of bulk Fe81Ga19 and Fe73Ga19Ni8 (at. %) ferromagnetic shape memory alloys (FSMAs). In the Fe81Ga19 FSMA, after solution treatment (ST) at 1100 °C for 4 h and quenching in ice brine, the antiphase boundary segments of the D03 domain were observed in the A2 (disordered) matrix. When the Fe81Ga19 FSMA was solution treated and aged at 750 °C for 24 h and then furnace cooled (FC), the A2 + D03 phase transformed into A2 + B2 + D03 structures, accompanied by coarse B2 + D03 precipitates in the A2 matrix. This result decreased the saturation magnetostriction of the aged Fe81Ga19 FSMA. However, adding more Ni to the Fe81−xGa19Nix (x = 8 at. % Ni) FSMAs enhanced the formation of B2 + D03 structures, further decreased the saturation magnetostriction, and destroyed the ferromagnetic shape memory effect in Fe73Ga19Ni8 FSMA ST, aged at 750 °C for 24 h, and FC.