| The Tb0.3Dy0.7Fe1.95 alloy was prepared by zone melting directionally solidified device. The variation and the relationship of the preferred orientation, the growth mode, the crystal morphology and the magnetostriction of the Tb0.3Dy0.7Fe1.95 alloy with different growth rates were studied;The crystal structure, microstructure and magnetostriction of the Tb0.3Dy0.7Fe1.95-xMx(x=0.03,0.06,0.09;M=Nb,Zr,Ti)alloys were systematically studied.Results demonstrated that with increase of the growth rate from 10μm/s to 380μm/s gradually, the axial preferred orientation of the Tb0.3Dy0.7Fe1.95 alloy changed from <110> orientation to <311> and mixed orientations <110> <211> and <533>, and later to the original <110> orientation. When the growth rate V≥350μm/s, the axial preferred orientation wasn't clear. In the whole process, two unstable transitional stages 180μm/s0.3Dy0.7Fe1.95 alloy was determined by the preferred orientation and the crystal morphology. When the growth rate was in the range of 50-180μm/s, the cellular crystal morphology and <110> preferred orientation made the alloys have the maximum magnetostriction(the averageλreached 1150ppm);The magnetostriction of the alloys growing with cellular-dendritic crystal morphology and <110> preferred orientation(250μm/s≤V≤270μm/s)was also high(the averageλwas 1100ppm);In the transitional stage(180-250μm/s), the magnetostriction decreased(the averageλwas 1000ppm);When the growth rate was too low(V≤30μm/s)or too high(V>270μm/s), the magnetostriction would decrease.The matrix of the Tb0.3Dy0.7Fe1.95-xMx(x=0.03,0.06,0.09;M=Nb,Zr,Ti)alloys consisted predominantly of the cubic Laves phase with MgCu2(C15-type)structure. After Zr,Ti addition, the lattice parameter of the Laves phase in the alloys decreased by substituting rare earth elements Tb and Dy. But Nb addition didn't substitute rare earth elements Tb,Dy and Fe atom. Additions of Nb,Zr and Ti have been found to be effective in suppressing the formation of the deleterious RFe3 phase. The concentration of the elements affected significantly the magnetostriction. The improvement in magnetostriction was maximum for the elements-added alloys with a low concentration of the elements(x=0.03) as compared to the parent alloy Tb0.3Dy0.7Fe1.95. However, the decrease in magnetostriction at a higher concentration(x=0.09)was due to the formation of paramagnetic phases, NbFe2,TiFe2 and Zr-rich,Re-rich affecting magnetostriction. Whereas the magnetostriction had little improvement as compared to the parent alloy Tb0.3Dy0.7Fe1.95. |
