Influence of magnetic flux density and cooling rate on orientation behavior of Tb0.27Dy0.73Fe1.95 alloy during solidification process

Abstract

The rare-earth giant magnetostrictive material Tb0.27Dy0.73Fe1.95 is one of the most important functional magnetic materials. Their superior properties include high saturation magnetostrictive coefficient at room temperature, high electromechanical coupling coefficients, high output power, fast response, high energy density, and non-contact drive. Thus, they can be used to build sensors, precision machinery, magnetomechanical transducers, and adaptive vibration-control systems. In this material, the magnetic phase (Tb, Dy)Fe2 has a typical MgCu2-type cubic Laves phase structure and exhibits different magnetostrictive properties along different crystal orientations. The 111 direction of this phase is the easy magnetization axis, along which the linear magnetostriction is higher than other directions. Thus, researchers have focused on preparing (Tb, Dy)Fe2 with a crystallographic orientation along or close to the 111 direction. Generally, the directional solidification method is used to prepare the Tb0.27Dy0.73Fe1.95 alloy. However, a crystal orientated along the 110 or 112 direction is always obtained and both of these directions require a high external magnetic field for improved magnetostrictive performance. The 111 preferred growth orientation can be acquired using seed crystal technology. However, the relatively low growth velocity can cause the appearance of the linear (Tb, Dy)Fe3 phase which induces a high brittleness of the material. Therefore, new methods to prepare Tb0.27Dy0.73Fe1.95 products with high 111 orientation at higher growth velocity are required. In this paper, we solidify the Tb0.27Dy0.73Fe1.95 alloys under various high magnetic field and cooling rate conditions. We study the effects of the magnetic flux density and cooling rate on the crystal orientation of the (Tb, Dy)Fe2 phase and the magnetization behavior of the alloys. It is found that after field-treated solidification, a high 111 orientation of (Tb, Dy)Fe2 along the magnetic field direction can be produced. As a consequence, the magnetostriction without applying stress remarkably increases. By increasing the magnetic flux density applied during the solidification of the Tb0.27Dy0.73Fe1.95 alloys, the 111 orientation of (Tb, Dy)Fe2 could be obtained at higher cooling rates. Ranging from 4 T to 10 T, with increasing cooling rate the magnetic flux density, at which the 111 or 110 orientation of (Tb, Dy)Fe2 occurs, increases or decreases, respectively. The saturated magnetization of the alloys increases with increasing cooling rate. The application of the magnetic fields does not affect the saturated magnetization.