Assessment of Directionally Solidified Eutectic Sm–Fe(Co)–Ti Alloys as Permanent Magnet Materials

Abstract

Sm–Fe–Ti and Sm–Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> –Ti alloys were prepared via arc-melting and directionally solidified on a water-cooled copper hearth. The as-solidified alloys featured cells of the Sm(Fe,Co,Ti) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> –Ti(Fe,Co) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+δ</sub> –(α-Fe) lamellar eutectic. The lamellae of Sm(Fe,Co,Ti) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> phase with a crystal structure of the ThMn12 type were less than 0.2 μm thick, and had their [001] easy-magnetization directions oriented along the temperature gradient of the solidification. The eutectic microstructure led to an increased coercivity, especially in the Co-added alloys. Below 250 °C, this coercivity was found not to vary much with temperature with a temperature coefficient of -0.18 %/°C. However, the modest absolute values, reaching only 0.7 kOe, are insufficient for utilization of the directionally solidified alloys as anisotropic permanent magnets.