Microstructure evolution and magnetic properties of the Nd sub(9)Fe sub(81-x)Ti sub(4)C sub(2)Nb sub(4)B sub(x) (x=11, 13, 15) bulk magnets prepared by copper mold suction casting

The bulk nanocomposite magnets of Nd sub(9)Fe sub(81-x)Ti sub(4)C sub(2)Nb sub(4)B sub(x) (x=11, 13, 15) in sheet form with the thickness of 0.7 mm were prepared by copper mold suction casting and subsequently annealing. The microstructure evolution and magnetic properties of bulk magnets were studied. It was shown that the as-cast microstructure of bulk alloys were composed of Nd sub(2)Fe sub(14)B, alpha -Fe, Fe sub(3)B crystalline phases and an amorphous matrix, and that the glass formability of alloy was improved with increasing the B content. The DSC analysis showed that the as-cast bulk alloys had the crystallization behavior of a two-step process. After annealing at the temperatures which was 40-63 K higher than their onset temperatures of the second exothermic peak, Nd sub(9)Fe sub(81-x)Ti sub(4)C sub(2)Nb sub(4)B sub(x) (x=11, 13, 15) bulk alloys obtained a finely mixed structure which were composed of Nd sub(2)Fe sub(14)B, alpha -Fe, Fe sub(3)B, (Nb, Ti)C crystalline phases and a residual amorphous phase, whose magnetic properties were significantly enhanced. For the bulk magnets of Nd sub(9)Fe sub(81-x)Ti sub(4)C sub(2)Nb sub(4)B sub(x) (x=11, 13, 15), the optimal magnetic properties of B sub(r)=0.63 T, sub(i)H sub(c)= 155.1 kA/m, (BH) sub(max)= 18.73 kJ/m super(3) could be achieved when x=13 after annealing at 983 K for 10 min.