SKOTNICOVÁ Kateřina VSB - Technical University

Preparation of Magnets Nd-Fe-B in using TbH2 and Study of their Structure and Magnetic Properties

Co-authors KOLCHUGINA Natalia B., LUKIN Aleksandr A., KURSA, Miroslav

The aim of work was the enhancement of coercivity of sintered Nd–Fe–B magnets without obvious reduction of the remanence by diffusing Tb onto the surface of the Nd2Fe14B matrix grains. We have studied the kinetics of TbH2 decomposition in terms of the possible application of the hydride as an effective addition for sintered Nd-Fe-B-based magnets. The diffusion dependence of the decomposition process was demonstrated; the complete decomposition of the TbH2 hydride takes place during heating to 1000°C. Two Nd-Fe-B magnets were prepared using strip-casting alloy (free from terbium), which was refined by hydrogen decrepitation process. Terbium hydride was added to the mixture (to 2 and 4% Tb concentration in the composition), which was milled in propyl alcohol, compacted, sintered at 1070°C, and subsequently heat treated at 500°C for 2 h. Before sintering, the mixture was passivated in nitrogen flow. The low hydrogen content in the magnets prepared in using TbH2 additions indicates the complete decomposition of the hydride and freeing Tb for introduction into a magnet during sintering the mixture. Electron-microscopic studies of the element composition of near-grain boundary regions and 2-14-1-phase grains and X-ray diffraction studies of the phase composition sintered magnets indicate the required distribution of components in the phases. The coercive force of the Nd-Fe-B magnets sintered in using TbH2 hydride was shown to be higher than that for magnets prepared from the initial Tb-containing alloy. The remanence of magnets prepared with the terbium hydride additions demonstrates the unusually moderate decrease with increasing terbium content.