Multiscale influence of trace Tb addition on the magnetostriction and ductility of 〈100〉 oriented directionally solidified Fe-Ga crystals

Abstract

New-generation magnetostrictive applications in micromanipulation instruments, torque sensing, and transducers require materials that offer a combination of large magnetostriction and good structural properties. $\mathrm{F}{\mathrm{e}}_{100\ensuremath{-}x}\mathrm{G}{\mathrm{a}}_{x}\text{-based}\phantom{\rule{4pt}{0ex}}(x=17--19)$ alloys are potential candidates. In this work, the solidification behavior of Tb-doped FeGa alloys is investigated by theoretical simulation and experimental observation; directional solidification parameters are optimized to obtain the largest solid solubility of Tb while keeping the $\ensuremath{\langle}100\ensuremath{\rangle}$ preferred orientation. The multiscale evolution of the structure with Tb additions that enhances both magnetostriction and tensile properties is systematically studied in alloys prepared under optimal directional solidification conditions. Magnetostriction of 387 ppm is accompanied by a remarkable tensile fracture strain of 12.5% in 0.05 at.% Tb-doped ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$. The values represent an improvement of $\ensuremath{\sim}29%$ in magnetostriction and a sixfold enhancement in tensile fracture strain compared with undoped binary ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$. The increase in magnetostriction is attributed to the higher density of tetragonally modified $\mathrm{D}{0}_{3}$ nanoinclusions induced by traces of Tb. The enhancement in ductility is explained by the dislocation concentration around the submicron-scale Tb-rich precipitates which can effectively hinder their motion. The FeGa alloys doped with traces of Tb can be easily processed to thin sheets or wires and are likely to be extensively applied because they contain only traces of rare earths.