Structure of melt-spun Fe-Ga-based magnetostrictive alloys

Fe_1-xGa_x (x=0.17, 0.21, 0.25 and 0.3) alloys were rapidly quenched by the melt-spinning technique to determine the maximum Ga concentration that retains the disordered bcc (α-Fe) phase at room temperature. The texture of the ribbons as a function of melt-spinning parameters and annealing was also extensively studied. All of the as-spun samples were found to be crystalline. For x=0.17, only the disordered bcc phase was found and for x=0.25 and 0.3, primarily DO₃ phase was found, while for x=0.21, the phase is bcc at high wheel speed and DO₃ at low speed. For the free side of the as-spun ribbons, the easy growth axis <100> of α-Fe or of DO₃ tilts about 10° to 20° from the ribbon normal and <011> is along the ribbon length. This texture does not change significantly with wheel speed. The texture on the wheel side of the ribbon is close to random at high speed but increases with slower speed. For Fe₈₃Ga₁₇, 900°C annealing reduces the tilt angle while 1100°C annealing recrystallizes the grains and produces strong <100> out of plane texture but randomizes the directionality in the plane. Annealing with sulfur addition was found to enhance the {100} texture but did not produce the desired <100> along the longitudinal direction of the ribbon. The saturation magnetostriction, λ_s, of as-spun Fe₇₉Ga₂₁ and Fe₈₃Ga₁₇ both having a disordered bcc structure and strong {100}<011> texture was measured as 98 and 130 ppm, respectively, along the ribbon length.