| In this dissertation, the phase transformation temperatures(or temperature intervals) and the nucleation undercooling of Nd2Fe14B/Fe3 B type nanocomposite Nd9Fe85-xTi4C2Bx(x=10~15) alloy ingots have been determinated by differential thermal analysis(DTA) method. With the help of X-ray diffraction(XRD), it have been studied that the development of the phase transformations of the solidification process of the ingot samples at cooling rate of 40K/min. On this basis, the Nd9Fe85-xTi4C2Bx(x=11, 13, 15) alloys with a size of 10mm×20mm×0.7mm were prepared by copper mold suction casting and subsequent annealing. The effects of boron content on the phase constitution, microstructure and magnetic properties have been investigated.The XRD results showed that the microstructures of the Nd9Fe85-xTi4C2Bx(x=10~15) alloy ingots were mainly composed of Nd2Fe14 B, Fe3 B, α-Fe, Nd1.1Fe4B4 and TiC, and they had the same phase compositions after DTA. The DTA results showed that the solidus temperatures(TS) of the alloy ingots gradually increased from 1353.5K to 1358.3K and the liquidus temperatures(TL) of them decreased from 1498.5K to 1472.5K with the increasing of B content. And the Nd9Fe85-xTi4C2Bx(x=10~15) alloy ingots have a greater degree of nucleation undercooling, which decreasd from 128.1K to 95.9K with the increasing of B content. The phase transformation temperatures(or temperature intervals) obtained at cooling have been shifted with the increasing of B content, simultaneously. On the basis of phase analysis, it may be stated that development of the phase transformations of the solidification process of the ingot samples at cooling rate of 40K/min can be described by the following scheme: Lâ†'γ-Fe,L+γ-Feâ†'Nd2Fe14B,Lâ†'Nd2Fe14B+Fe3B,Lâ†'Nd2Fe14B,Lâ†'Nd2Fe14B+Fe3B+Nd1.1Fe4B4.The XRD results showed that the microstructures of as-cast Nd9Fe85-xTi4C2Bx(x=11, 13, 15) alloys by copper mold suction casting were mainly composed of Nd2Fe14 B, Fe3 B, α-Fe, Nd1.1Fe4B4 and TiC. And the average grain sizes of the as-cast alloy samples can be estimated to be about 46nm(x=11), 44nm(x=13), 39nm(x=15), respectively. With the B content increased, the XRD pattern peak of the Nd9Fe85-xTi4C2Bx(x=15) alloy has been broadened, which indicated that the grain sizes became finer or even the amorphous phase appeared. Furthermore, the morphology observation of the microstructure of as-cast Nd9Fe85-xTi4C2Bx(x=15) alloy indicated that the existence of an amorphous phase. The microstructure of the Nd9Fe85-xTi4C2Bx(x=11, 13, 15) alloys annealed at 913 K and 953 K for 10 min are mainly composed of Nd2Fe14 B, Fe3 B, α-Fe, Nd1.1Fe4B4 and TiC. Although the phases compositions did not be different with those before annealing, the relative amount of Nd2Fe14 B and Fe3 B in the annealed alloys increased to a higher extent with the increasing of the content of B.The as-cast Nd9Fe85-xTi4C2Bx(x=11, 13, 15) alloys showed a weak hard magnetic, the value of iHc is from 46.30kA/m to 83.52kA/m and the Mr from 0.20 T to 0.31 T. For the as-cast Nd9Fe85-xTi4C2Bx(x=11, 13, 15) alloys, the optimal magnetic properties of(BH)max=5.33kJ/m3, iHc=83.52kA/m, Mr=0.31 T could be achieved when x =15.The magnetic properties of Nd9Fe85-xTi4C2Bx(x=11, 13, 15) alloys annealed at 913 K for 10 min have not been improved. However, magnetic properties of Nd9Fe85-xTi4C2Bx(x=11, 13, 15) alloys annealed 953 K for 10 min have been enhanced to different extent with the increasing of B content. For the Nd9Fe85-xTi4C2Bx(x=11, 13, 15) alloys annealed at 953 K for 10 min, the optimal magnetic properties of(BH)max=9.36kJ/m3, iHc=122.06kA/m, Mr=0.39 T could be achieved when x=15. |
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