Magnetic properties, phase and microstructure of direct cast Nd9.5Febal.Co10MB15 rod magnets

Abstract Nd 9.5 Fe bal. Co 10 MB 15 (M=Ti 2.5 Zr 0.5 , Ti 2.5 Nb 0.5 , Zr 2.5 Nb 0.5 , Nb 2.5 Zr 0.5 ) rod magnets are prepared by direct casting method. Thermo-gravimetric analysis results show that minor soft α -(Fe, Co) phase coexists with magnetically hard 2:14:1 phase in the above magnets. In addition, amorphous phase is also observed in magnets with Ti 2.5 Zr 0.5 and Nb 2.5 Zr 0.5 addition. According to differential scanning calorimetry results, obvious exothermic peaks are observed in the magnets with Ti 2.5 Zr 0.5 and Nb 2.5 Zr 0.5 addition. Meanwhile, the crystallization behavior of the amorphous phase is a two-step process. The activation energies of magnets with Ti 2.5 Zr 0.5 and Nb 2.5 Zr 0.5 addition are 542 kJ/mol and 558 kJ/mol, respectively. Microstructure images show that the 2:14:1 phase is surrounded by boron-rich grain boundary phase. The average grain size of 2:14:1 phase in Nb 2.5 Zr 0.5 -doped magnets is smaller than in Ti 2.5 Zr 0.5 -doped magnets. Magnetic measurements show that larger coercivity is observed in both Ti 2.5 Zr 0.5 -doped magnet and Nb 2.5 Zr 0.5 -doped magnet, while better squareness of the demagnetization curves and higher magnetic energy product are obtained in Ti 2.5 Nb 0.5 -doped magnet.