Magnetic Properties And Microstructure Of (Ce,Nd)-Fe-Co-B-M(M=Ti,Zr)Rare-earth Permanent Alloys

Nd-Fe-B magnets have been widely used owing to the excellent magnetic properties,which lead to the sharply consumption of the critical raw material as Pr,Nd,Dy,Tb,whereas La,Ce with high abundance and low cost are stacked largely.Research works show that the substitution for Nd by using the abundant rare earth metals such as Ce can help develop low-cost permanent Nd-Fe-B magnets.It is of great significance to save the key element Nd and for the development of Nd-Fe-B industry.Aiming at low cost and high performance of rare earth permanent magnets,the theme of this work has a discussion from the aspects of partial and total substitution of Ce for Nd.The addition of Ti element for the(Nd,Ce)-Fe-Co-B alloys are designed and prepared by melt-spinning method,it shows that the Ti addition has proved to result in relevant improvements in the magnetic properties.In order to further improve the magnetic properties of(Nd,Ce)-Fe-Co-B alloys,the Ti and Zr doped nanocomposite alloys with low rare-earth are prepared by amorphous crystallization method.The effects of Ti and Zr addition on the magnetic properties,microstructure and the coercivity mechanism of the alloys are studied.Meanwhile,the Ce-Fe-Co-Zr-B nanocrystalline alloys have been investigated by optimizing process parameters.The effects of annealing temperature on magnetic properties,exchange coupling effect and domain structure of the alloy are analyzed.This study provides theoretical guidance for the preparation and industrial production of high-performance and low-cost permanent magnets.The main conclusions are listed below:(1)The(Nd0.7Ce0.2)2Fe12Co2-xBTix(x=00.6)alloys are prepared by melt-spinning method.It shows that the intrinsic coercivity Hcj,maximum energy product(BH)max and and squareness Hk/Hcj present the tendency that increase first and then decrease with increasing x.The optimal magnetic properties are obtained for alloy with x=0.4:Hcj=7.13 kOe,Br=9.99 kG,Hk/Hcj=0.38,(BH)max=16.23 MGOe.A certain amount of Ti addition could cause a uniform distribution of hard magnetic phase grains and increase domain width Dw,as the Dw increases from 40-80 nm to 60-140 nm.Compared with the Ti-free alloy,the Ti-doped(x=0.4)alloy possesses a lower Hr/Hc,a higher maximum p of the 3-D diagrams and the highest magnitude of the positive δM peak,which reflects the stronger exchange coupling and better magnetic performance.(2)The[(Nd0.8Ce0.2)1.6Fe12Co2B]100-xTix(x=0,0.5,1.0,1.5,2.0 wt%)nanocomposite alloys are prepared by melt-spinning method and subsequent thermal annealing.The optimal magnetic properties are obtained for Ti-0.5 alloy:Hcj=5.58 kOe,Br=9.6 kG,(BH)max=14.5 MGOe.A small amount of Ti addition can refine hard magnetic phase grains and reduce a-Fe soft magnetic phase.Meanwhile,it causes a uniform distribution domain structures and increases domain width Dw.Compared with the Ti-free alloy,the Ti-doped(x=0.5)alloy possesses a higher nucleation field(Hn)and the maximum magnitude of the positive δM peak,confirming the strongest magnetic interaction between the grains and resulting in the optimal magnetic properties(3)The[(Nd0.8Ce0.2)1.6Fe12Co2B]100-xZrx(x=0,15 2,3,4,5 wt%)nanocomposite alloys are prepared by melt-spinning method and subsequent thermal annealing.The glass forming ability of as-spun ribbons is improved by Zr addition.The optimal magnetic properties are obtained for the Zr-3 alloy:Hcj=5.99 kOe,Br=9.5 kG,Hk/Hcj=0.38,(BH)max=15.2 MGOe.Compared with the Zr-free alloy,the Zr-3 alloy possesses a smaller grain size and uniform distribution of soft magnetic a-Fe phase.The results of Kronmuller plot show that nucleation model is the dominating mechanism for the magnetization reversal in the Zr-0 and Zr-3 alloys and give the evidence for the increase in microstructural parameter aex resulting in a drastic increase of coercivity in the Zr-doped alloy.The FORC diagrams suggest the Zr-doped sample with a higher maximum p of the major peak and the flat surface is responsible for the optimal magnetic performance.(4)The Ce17Fe76.5Co1Zr0.5B6 alloys are prepared by melt-spinning method and subsequent thermal annealing.The enhanced coercivity Hcj of 6.32 kOe and maximum energy products(BH)max of 5.52 MGOe have been obtained for the Ce17Fe76.5Co1Zr0.5B6 alloys at the optimal annealing temperature of 793 K and 853 K,respectively.The results of the magnetization reversal behaviors suggest that nucleation model is the dominating mechanism for the high coercivity and high maximum energy product alloys.The results of the magnetic domains analysis show that the high maximum energy product(annealed at 853 K)sample possesses higher domain width Dw(0.24 ± 0.01 μm)and domain wall energy γw(2.93 ± 0.12 erg/cm2).