Iron nitride based magnetic powder synthesized by mechanical alloying of Fe-based glassy powders and solid nitrogen compounds

Abstract

Iron nitrides composed of abundant and inexpensive Fe and N compounds such as α′′-Fe16N2 and γ’-Fe4N are in the spotlight as potential magnetic materials for the next generation of electric vehicles. Extensive applications of iron nitrides, however, have not been reported since their mass production is yet to be established. Due to the low solubility of nitrogen in liquid iron, the production of iron nitrides through conventional steelmaking processes is difficult. Moreover, α′′-Fe16N2 with a high saturation magnetization is known to be metastable and can form below 200 °C where diffusional phase transformations are slow. In this study, we propose a nonequilibrium process that can enhance the kinetics for iron nitride formation at low temperatures. Thermodynamically metastable Fe-based glassy alloy with a relatively open atomic packing structure was used as the starting material. Synthesis of iron nitrides during the mechanical alloying of Fe-based amorphous powders and solid nitrogen compounds was systematically studied to understand the mechanism of solid state nitriding reactions. In addition, thermal and magnetic properties were studied to provide a basis for practical applications of iron nitrides as rare-earth free magnetic materials.