Fundamental Properties Of Rapidly Quenched Y-Fe-B Alloys And The Effects Of Nd/Gd Substitution

Nd Fe B magnets are widely used in electric vehicles,wind power generation,medical devices,aerospace,electrical machinery and many other fields due to their excellent hard magnetic properties.With the increasing use of Nd Fe B magnet,the consumption of rare earth elements such as Pr,Nd,Dy and Tb has been rising.At the same time,the abundant rare earth elements represented by La,Ce and Y have not be fully utilized,which leads to the unbalanced application of rare earth resources.In this work,aiming to develop rare-earth permanent magnets based on high-abundance rare earth element yttrium（Y）,the phase precipitation behavior,magnetic properties and thermal stability of ternary Y-Fe-B alloys have been investigated systematically.The substitution of neodymium（Nd）and gadolinium（Gd）for Y to improve the magnetic properties and corrosion resistance of Y-Fe-B alloy have also been studiedconducted.Firstly,Y₂Fe₁₄B alloys were prepared by melt-spinning process,and the effects of phase precipitation behavior,magnetic properties and microstructure of Y₂Fe₁₄B alloys prepared at different wheel speeds and heat treatments were investigated.The Y₂Fe₁₄B alloys prepared at low wheel speeds of 10 m/s and 20 m/s show low hard magnetic properties with soft magnetic phase ofα-Fe precipitated.The samples prepared at 30 m/s and 40 m/s have fine grains and good magnetic properties.Hard magnetic phase Y₂Fe₁₄B can be detected in Y₂Fe₁₄B alloys prepared at 10～40 m/s.The alloy prepared at 50 m/s consists of amorphous phase with decreased magnetic properties decrease.It is found that the optimized hard magnetic properties can be obtained in a relatively wide range of wheel speeds for Y₂Fe₁₄B alloy,which is different from Nd-Fe-B alloy.The the alloy prepared at 36 m/s exhibits the magnetic propertieswith saturation magnetic polarization J_s=1.43 T,remanence J_r=0.88 T,coercivity H_cj=149 k A/m,and maximum energy product（BH）_max=6.8 MGOe.The microstructure analysis shows that the Y₂Fe₁₄B grains are uniformly distributed in the optimized alloy and the grain is between 20-50 nm.There is no grain boundary phase or second phase.The phase precipitation behavior of amorphous Y₂Fe₁₄B alloy during heating treatment was investigated.It was found thatα-Fe precipitated first from the matrix at 249°C,then the Y₂Fe₁₄B hard magnetic phase precipitated at 606°C.When increasing the temperature to 816°C,Fe_xB phase precipitated and the alloy is composed ofα-Fe,Y₂Fe₁₄B and Fe_xB phases.For the alloys annealing at 500-800°C,the coercivity increases with the annealing temperature and reaches a maximum value at 700°C.Further increasing the temperature leads to reduced coercivity due to the growth of grains.The hard magnetic properties of the alloys after heat treatment are significantly lower than the optimized melt-spun alloy due to the existence of various precipitation phases.Secondly,in order to improve the magnetic properties,melt-spun(Y_1-xNd_x)₂Fe₁₄B（x=0-1）alloys were prepared,and the effect of Y substitution by Nd on phase structure,magnetic properties and corrosion resistance have been studied.The results show that Y substitution by Nd can improve the hard magnetic properties significantly,and the coercivity of(Y_0.5Nd_0.5)₂Fe₁₄B alloy reaches 416 k A/m.Y₂Fe₁₄B has a positive coercivity temperature coefficient in a certain range of temperature.The substitution of Nd will reduce the temperature stability in some extent,but it can still obtain excellent thermal stability in partially substituted alloys.The substitution of Nd can also enhance the exchange coupling effect and reduce the openness of the recoil loops.In addition,the effect of rare earth content on phase structure and magnetic properties of(Y_1-xNd_x)_yFe₁₄B（x=0-0.5,y=2.5,3）alloys have been invesgated.The results show that YFe₂ phase appears in Y₃Fe₁₄B.The increase of RE content will improve the coercivity.The coercivity of melt-spun Y₃Fe₁₄B is 281 k A/m.In order to further improve the thermal stability,melt-spun(Y_1-xGd_x)₂Fe₁₄B（x=0-1）alloys were prepared,and the effect of the Y substitution by Gd on phase structure,magnetic properties and thermal stability have been studied.The results show that Gd atoms occupy the position of Y atoms in crystal structure 2:14:1 phase,which increases the lattice parameters.Gd substitution slightly increases the coercivity and reduce the saturation magnetization,remanence,and maximum energy product.All(Y_1-xGd_x)₂Fe₁₄B（x=0-1）alloys have positive coercivity temperature coefficients.With the increase of temperature,the coercivity increases in different ways for the various compositions,indicating that these alloys have excellent high temperature stability.In addition,The substitution of Gd can increase the corrosion potential and decrease the corrosion current density 3.5 wt.%Na Cl solution,leading to the improved corrosion resistance.The present work clarifies the basic behavior of Y-based rare-earth permanent magnet based on the investigations of ternary Y-Fe-B alloys and quaternary alloys substituted by Nd and Gd.It is meaningful for developing high abundant rare-earth permanent magnets with excellent properties and promoting the balanced utilization of rare earth resources.