Materials Research Express (Jan 2020)
Solidification microstructure and phase transition of La-Nd-Fe alloys
Abstract
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( γ -Fe) and then follow by the formation of bcc( α -Fe) and/or Fe _17 Nd _2 phases through different peritectic reactions. The solidification microstructure of three Fe _65 La _29 Nd _6 , Fe _65 La _25 Nd _10 and Fe _65 La _22 Nd _13 alloys presents three-phase microstructure with bcc( α -Fe), Fe _17 Nd _2 and fcc(La,Nd) phases, while that of three Fe _65 La _19 Nd _16 , Fe _65 La _9 Nd _26 and Fe _65 La _15.5 Nd _19.5 alloys shows three-phase microstructure with bcc( α -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 Fe _65 La _12 Nd _23 , Fe _65 La _6.5 Nd _28.5 , 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.
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