Development of ultra-fine grain sized SmFe12-based powders using hydrogenation disproportionation desorption recombination process

Abstract

SmFe12-based compounds possess promising intrinsic magnetic properties, even superior to those of Nd2Fe14B phase at elevated temperatures. However, the remaining challenge is to demonstrate that those intrinsic properties can be further developed into practically relevant extrinsic ones by proper processing. Here we have employed hydrogenation disproportionation desorption recombination (HDDR) process for preparation of ultrafine-grained SmFe12-based alloys with the tetragonal ThMn12-type crystal structure. The effect of alloying elements and grain boundary phase on disproportionation rate is investigated and experimental HDDR process phase diagram is proposed. Due to the high vapor pressure of Sm as well as the competing phases, recombination into phase-pure samples can be realized only in a narrow processing parameters window. The resultant phase constitutions, chemical composition, microsctructure and crystallographic relations at different process steps are discussed.