Nanostructure Evolution in Fe₃B/Nd₂Fe₁₄B Nanocomposite Permanent Magnets and Effects of Ti-C Additions

Abstract

The continuous cooling curves during melt-spinning process of typical Fe₃B/Nd₂Fe₁₄B-type nancomposite permanent magnet alloys Nd₄Fe_77.5-xT_xB_18.5 where T is Cr or Cu were measured using the infrared imaging technique and a continuous cooling transformation (CCT) diagram was constructed. The CCT diagram suggested that the effect of T was kinetic and phase selective. Effects of Ti and C additions on phase selection during rapid solidification were investigated in a Nd-poor and B-rich concentration region where the unfavorable Nd₂Fe₂₃B₃ metastable phase becomes prevailing. The Ti-C addition was found to promote crystallization of Nd₂Fe₁₄B and prevents formation of γ-Fe. Utilizing this knowledge, a series of high coercivity Fe-B/Nd₂Fe₁₄B-type nanocomposite permanent magnets were developed on the basis of Nd-Fe-B-Ti-C system.