Preparation, Microstructur And Magnetic Properties Of Nd₂Fe₁₄B/Fe₃B-type Nanocomposite Magnets

Nanocomposite magnetic materials are consisted from nano-scale hard magneticphase and the connection with soft magnet phase, usually lead to excellent magneticperformance. Due to unusually high saturation magnetization and high anisotropicfield, the nanocomposite magnetic materials required a less of amount of an expensiverare earth elements and have the potential to be new kind of permanent magnet infuture.In this work, the Nd₂Fe₁₄B/Fe₃B-type nanocomposite magnets have beenprepared by rapid solidification and melt spinning with subsequent crystallizationannealing. The effects of alloy composition and crystallization treatment on the phaseconstitution and magnetic properties have been investigated systemically. X-raydiffraction, Differential Scanning Calorimeter and Physics Property MeasurementSystem have been used for study of materials. Special attention has been focused tooriginal microstructure, crystallization behavior and magnetic performance of high Bcontent composition.Nd₉Fe_77-xB_10+xNB₄（x=1⁷） ribbons were fabricated by melt spinning at speed of15m/s. The resistance of crystallization increases with increasing B content.Amorphous phase was transformed to Nd₂Fe₁₄B/Fe₃B-type nanocomposite magnetsafter crystallization annealing process. These Nd₂Fe₁₄B/Fe₃B-type magnets exhibittwice magnetization reversal because the microstructure can not satisfy the idealexchange-coupled mode. This issue can be solved by modification of the alloycomposition and heat treatment. For Nd₉Fe_77-xB_10+xNB₄（x=1⁷） magnets, thesamples with x=2or3exhibit the higher volume fraction of Fe₃B phase、saturationmagnetization、remanence compared with samples with x=1. When the B contentincreases from13at.%to14¹6at.%（the content of iron decrease to71at.%）, thevolume fraction of magnetic phase decreases, the reason is a less amount of Fe atomswhich leads to decreasing of saturation magnetization. Otherwise the residualneodymium atom can form the Nd-rich phase. These Nd-rich phase distributing in thegrains can contribute to the obviously improvement of coercivity. Non-magnetic boride phase will be formed if the B content increases up to17at.%continuously.Nd_6.0-xY_xFe₆₈B₂₄Nb₂alloy has good GFA due to high content of boron. Originalamorphous microstructure consisting of Nd_1+εFe₄B₄cluster is achieved during themelt spinning, even by a relative low cooling rate. B-rich phase and-Fe phase areprecipitated among amorphous matrix after annealed at high temperature for10min.Nd6.0-xYxFe68B24alloy （2mm diameter rod） were fabricated by the rapid solidification.The performance of2mm diameter rod is not satisfactory which is caused by themajor phase of the as-casted rod and the lacking of hard magnetic phase Nd₂Fe₁₄B.For Nd6.0-xYxFe68B24alloy of2mm diameter rod, the Y substitution for Nd leads todecreasing of the magnetic performance, because the anisotropic field of Y is lowerthan Nd. The coercivity, remanence and magnetic energy product are decreased withincreasing of the Y content.Both Nd_5.5Y_0.5Fe₆₈B₂₄Nb₂Balloy of1mm diameter rod and Nd6.72Fe65.28B24Nb4alloy of2mm diameter rod were fully amorphous. For BMG of Nd_5.5Y_0.5Fe₆₈B₂₄Nb₂B,the crystallization behavior is a two-step process. Soft magnetic phase Fe₃B and hardmagnetic phase were precipitated at677℃,750℃, respectively. After annealed at750℃for10min, the magnets have exhibited the most optimization magnetic properties:Hc=168.2kA/m, J_r=0.41T, M_s=1.08T,（BH）_max=9.8kJ/m³. The major factor ofdecreasing the magnetic properties is the formation of non-magnetic phase boride,which can be attributed to the high B content.