Solidification microstructure and phase transition of La-Nd-Fe alloys

The solidification microstructure and phase transition of ten La-Nd-Fe alloys were studied experimentally by scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS) and differential thermal analysis (DTA). Phase compositions and phase transition temperatures of La-Nd-Fe alloys were measured and the formed phases were identified. The solidification behavior of La-Nd-Fe alloys was analyzed based on the experimental results of both solidification microstructure and phase transitions with the reported Nd-Fe, La-Fe and La-Nd sub-binary phase diagrams. The results indicated that the solidification processes of all La-Nd-Fe alloys begin with the precipitation of primary phase fcc(gamma-Fe) and then follow by the formation of bcc(alpha-Fe) and/or Fe(17)Nd(2)phases through different peritectic reactions. The solidification microstructure of three Fe65La29Nd6, Fe(65)La(25)Nd(10)and Fe(65)La(22)Nd(13)alloys presents three-phase microstructure with bcc(alpha-Fe), Fe(17)Nd(2)and fcc(La,Nd) phases, while that of three Fe65La19Nd16, Fe(65)La(9)Nd(26)and Fe(65)La(15.5)Nd(19.5)alloys shows three-phase microstructure with bcc(alpha-Fe), Fe(17)Nd(2)and dhcp(La,Nd) phases. The two-phase micorstructure with Fe(17)Nd(2)and dhcp(La,Nd) ohases was formed in the solidification microstructure of four Fe65La12Nd23, Fe65La6.5Nd28.5, Fe(65)La(4)Nd(31)and Fe(65)La(1.5)Nd(33.5)alloys. Moreover, no stable ternary intermetallic compound was found in the present experiments. The solidification microstructure and phase transition of La-Nd-Fe alloys would provide a basis for the design of La-Nd-Fe-B magnetic alloys.