Anomalous phase transformation in magnetostrictive Fe₈₁Ga ₁₉ alloy

In this work, we have investigated the room-temperature phase constitution of heat-treated Fe₈₁Ga₁₉ alloys cooled from 800 °C at different rates. Results show that at cooling rates in the range from 0.43 to 0.26 °C/min, in addition to the A2 matrix, an fcc phase also can be observed in Fe₈₁Ga₁₉ samples at room temperature. To investigate the precipitation of the fcc phase out of A2 matrix, a systematic study of phase constitution was carried out on the samples quenched from different temperatures during cooling from 800 °C at 0.32 °C/min, which reveals an anomalous phase transformation between A2 and fcc. Precipitation of the fcc phase from A2 matrix occurs at 500 °C and its volume fraction exhibits a sharp increase at 400 °C. However, it begins to dissolve when further decreasing the temperature and only a minor fcc phase can be retained at room temperature, which suggests that the fcc phase is metastable below 400 °C. Magnetic measurements indicate that the precipitation of fcc phase deteriorates the saturation magnetization of Fe₈₁Ga₁₉.