DEFECTS IN TERFENOL-D CRYSTALS

The detailed microstructure of Terfenol-D (Tb0.27Dy0.73Fe1.95) single crystals, prepared by the Czochralski method using an induction-heated cold crucible, and a vertical float zoned Terfenol-D (Tb0.27Dy0.73Fe1.9) rod has been studied by transmission electron microscopy (TEM). It is found that the single crystal prepared with the Czochralski method has a primary growth direction within 8-degrees close to <112> and contains many fine Widmanstatten precipitates (WSP) distributed homogeneously across the crystal. On the other hand, the vertical float zoned rod consists of a few misorientated grains with dendritic morphologies and some rare earth-rich phases. TEM observation reveals that both types of crystals contain numerous {111} stacking faults. The vertical float zoned crystal contains a higher density of defects and a few interior oxide particles. Twins have been observed in the vertical float zoned crystals. The Widmanstatten needle phases in the crystal grown with the Czochralski technique are enclosed in interfacial dislocation networks, which are considered significantly to deteriorate the magnetostrictive properties.