Nd9Fe85-xTi4C2Bx (x=10–15) magnetic alloys were investigated by differential thermal analysis and X-ray diffraction analysis. The results showed that with the B content increasing from 10 at.% to 15 at.%, the liquidus temperatures TL of the alloys decreased from 1498.5 to 1472.5 K; the solidus temperatures TS of them increased from 1353.2 to 1358.3 K; and the nucleation undercooling of the alloy melts cooled at the rate of 40 K/min decreased from 122.8 to 95.9 K, resulting in the solidification structures consisting of Nd2Fe14B, Fe3B, α-Fe, Nd1.1Fe4B4 and TiC nanocrystallines. Furthermore, the Nd9Fe85-xTi4C2Bx (x=11, 13, 15) bulk alloys in sheet form with the thickness of 0.7 mm were prepared by copper mold suction casting and their solidification characteristics and solidification structures under sub-rapidly cooling rate were investigated. The results showed that partially amorphous structures were obtained in the as-cast bulk alloys and the amount of amorphous decreased with the increase of the B content. By annealing the as-cast bulk alloys at 923 K for 10 min, the nanocomposite microstructures composed with Nd2Fe14B, Fe3B and α-Fe nanocrystallines, which showed a single-phase hard magnetic behavior and enhanced magnetic properties, were achieved.DTA heating and cooling curves of Nd9Fe85–xTi4C2Bx (x=10–15) alloy ingots (at heating and cooling rate of 40 K/min) with marking of characteristic temperatures (Nd9Fe71Ti4C2B14)

The effects of melt overheating degree on the undercooling degree and resultant solidification structures of Nd9Fe85–xTi4C2Bx (x=10, 12) glass-forming alloys were studied by differential thermal analysis combining with solidification structure analysis. The results indicate that the undercooling degree of Nd9Fe85–xTi4C2Bx (x=10, 12) alloys significantly increases with the rise of melt overheating degree, and two overheating degree thresholds corresponding to the drastic increase of the mean undercooling degree are found for each of the alloys. The existence of two turning points of the mean undercooling degrees can be linked to the structure transitions inside the overheated melts, which result in the evident increase of volume fraction of amorphous phase in the solidified structures.

The bulk nanocomposite magnets of Nd9Fe81–xTi4C2Nb4Bx (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 Nd2Fe14B, α-Fe, Fe3B 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, Nd9Fe81–xTi4C2Nb4Bx (x=11, 13, 15) bulk alloys obtained a finely mixed structure which were composed of Nd2Fe14B, α-Fe, Fe3B, (Nb,Ti)C crystalline phases and a residual amorphous phase, whose magnetic properties were significantly enhanced. For the bulk magnets of Nd9Fe81–xTi4C2Nb4Bx (x=11, 13, 15), the optimal magnetic properties of Br=0.63 T, iHc=155.1 kA/m, (BH)max=18.73 kJ/m3 could be achieved when x=13 after annealing at 983 K for 10 min.Room temperature hysteresis loops of Nd9Fe81-xTi4C2Nb4Bx(x11, 13, 15) bulk samples aS-cast and annealed optimally