Research Progress of(Nd,Ce,La)-Fe-B Melt-Spun Ribbons
The continually growing demand for Nd-Fe-B magnets in the areas of wind power,electric motors,hybrid vehicles,medi-cal instruments,magnetic separation,and electronic communication devices,etc.has greatly accelerated the depletion of critical rare earth elements including Nd,Pr,Dy and Tb,etc.,which results in the rising prices of those low abundant rare earth elements,and a large backlogging of high-abundance and low price rare earths of Ce and La.Recently,in order to make balanced and efficient use of rare earth resources of Ce and La,a lot of research and development work was carried out on Ce,La or La-Ce doped(Nd,Ce,La)-Fe-B based permanent magnets.It was found that permanent magnets containing Ce or/and La could not only reduce the cost,but also pos-sessed an abnormal increase in the intrinsic coercivity when Ce content was 20％～30％(atom fraction)or La and La-Ce contents were about 10％,and satisfactory magnetic properties when Ce or/and La content was less than 50％,showing a very broad application pros-pect.This paper reviewed the research progress in related fields,which included the following issues.(1)Ce-Fe-B intrinsic properties and structure.Ce-Fe-B magnets had the same crystal structure as Nd-Fe-B,but they possessed much lower saturation magnetizations(4πMs),magnetocrystalline anisotropy fields(H)and Curie temperature(Tc).Ce-Fe-B-based permanent magnetic materials were mainly composed of Ce2Fe14B phase and some minor boundary phases such as CeFe2,Ce2Fe7,Ce2Fe5,Ce2Fe17,Ce-rich phase,B-rich phase,Fe-rich phase and cerium oxide.These boundary phases present were associated with the alloy compositions and preparation conditions,deteriorating the magnetic properties.(2)Research progress of Ce-Fe-B melt spun ribbons,focusing on the magnetic prop-erties,microstructure and phase precipitation behavior.Generally,for Ce-Fe-B melt spun ribbons,a proper heat treatment process is needed,which could benefit to decrease or inhibit the harmful phases present,and to optimize the microstructure.In most cases,Ce17Fe78B6 melt spun ribbons could exhibit better magnetic properties,such as remanence Br=0.69 T,coercivity Hcj=493.4 kA·m1,and maximum magnetic energy product(BH)max=68.4 kJ·m-3.Therefore,it had potential to be prepared as permanent magnets with the properties between the rare earth permanent magnets and the ferrite magnets.(3)Research progress of(Nd,Ce)-Fe-B melt spun rib-bons,focusing on the abnormal coercivity,phase separation and element segregation.So far,many researchers reported that Hcj of Ce doped Nd-Fe-B was significantly greater than that of pure Nd-Fe-B magnets when 20％～30％Ce substitution for Nd.In addition,some literature also reported the abnormal increase of Hc in 20％～30％Ce doped Nd-Fe-B ribbons,but H values was still lower than that of the melt spun ribbons without Ce addition.With the increase of Ce content,the decline rate of Hc was not constant.When Ce content x was less than 50％,H decreased slowly and its value was relatively high.However,when x=50％～100％,Hcj decreased relatively quickly.This showed that it was absolutely possible that using Ce partly substitution for Nd produces low cost and high performance permanent magnets.(4)Research progress of(Nd1-xREx)2Fe14B(RE=La,La-Ce)melt spun ribbons.The microstructure and magnetic properties of La and La-Ce doped Nd-Fe-B melt-spun ribbons were summarized.Compared with Ce-Fe-B permanent magnets,there was relative less literature about RE-Fe-B(RE=La,La-Ce)magnets.Due to the large glass forming ability,La-Fe-B alloy was diffi-cult in forming 2∶14∶1 phase of La2Fe14B.In(Ce1-xLax)2Fe14B ribbon magnet,over 80％La substitution led to the decomposition of 2:14:1 phase.However,partial substitution La for Ce(x＜50％)could effectively enhance the hard magnetism and thermal stability.Adding Nd(≥30％)benefited the formation of 2∶14∶1 phase and magnetic properties of the La-based magnets.La-doped Nd-Fe-B samples had better performance with doping amount less than 50％.In general,magnetic properties of La-Ce co-doped samples were superior to those with La or Ce single-doped Nd-Fe-B ribbons.Some researchers reported that an abnormal increase of Hcj occurred in Nd-Fe-B alloys doped by 10％La or La-Ce.As a result,application of La-Ce co-doping could be considered to prepare Nd-Fe-B based magnets.In the end,the future development trend was prospected.Hopefully,high performance and cost-effective Nd-Fe-B-based per-manent magnets containing Ce,La or La-Ce elements could be prepared if we could make full use of the abnormal coercivity variation and composition's inhomogeneity.
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