Directional solidification of Tb-Dy-Fe magnetostrictive alloy

Grain-aligned rods of the huge magnetostrictive Tb-Dy-Fe alloy have been prepared by directional solidification techniques. Axial grain orientation, phase spacing and elemental distribution of the alloy rods have been investigated. It was found that unseeded rods usually show a strong [112] orientation at higher growth rate regime. At lower growth rate regime, [110] axial grain orientation was often observed. In all the rods, a range of phase spacing existed. The average spacing was more sensitive to the temperature gradient than the growth rate. Large spacing was achieved with lower temperature gradient and lower growth rates. It was also found that different partition of Tb and Dy in the Laves phase and RE-rich phase existed, as well as the microsegregation of Tb and Dy. These led to a higher Tb/Dy atomic ratio in the RE-rich phase and a variation of the Tb/Dy ratio in the cellular Laves phase sheets. To explain the different axial grain orientations, a model was proposed. An orientation selection principle was adopted such that an orientation with a higher local interface temperature among competing orientations was preferred. The effects of the kinetic attachment anisotropy and the surface tension anisotropy were considered.