Study On Rich Rare-Earth Phase Of Die-upset Nd-Fe-B Magnets

In this paper,the die-upset method’s influence for the orientation degree,microstructures and coercive force of the Nd_10.5Pr_2.5Fe₈₀Nb₁B₆ and Nd₆₇Cu₃₃/Nd_10.5Pr_2.5Fe₈₀Nb₁B₆ allies were studied.The excellent orientation degree and coercive force of die-upset magnets can be made through optimizing the die-upset technical.The influence of the hot-deformation temperature and press to the orientation degree of Nd_10.5Pr_2.5Fe₈₀Nb₁B₆ die-upset magnet were studied.α,the angle between the equivalent easy magnetization axis of the magnets and the die-upset pressure direction,was calculated.The α is represent for the orientation degree of the magnet.The larger of the α,the better of the orientation degree.The α decreased from 26.0 ° to 9.1 ° and the orientation degree become better when the hot-deformation temperature and press increase.The equiaxial crystals in the magnets decrease,the number of lamellar structure increases and the orientation degree of c axis increases as the αdecreases.The（004）peak appears and the orientation degree increases when the deformation ratio increases to 70 %.It is better for the secondary densification of the magnets when the deformation ratio increases.The influence of the mass fraction content of Nd₆₇Cu₃₃ to the orientation degree of Nd₆₇Cu₃₃/Nd_10.5Pr_2.5Fe₈₀Nb₁B₆ die-upset magnets were studied.The dual alloy powder consisting of alloy Nd_10.5Pr_2.5Fe₈₀Nb₁B₆ and 3 wt.%,6 wt.%,9 wt.% Nd₆₇Cu₃₃ was hot pressed at 993 K under150 MPa for 2 min,and then the hot-pressed precursors were deformed at temperature of 1143 K for 5 min with deformation ratio of 70 %.The die-upset magnets form a weak anisotropy of c axis at different mass fraction content of Nd₆₇Cu₃₃.The（Nd,Pr）Cu phase generates after adding Nd₆₇Cu₃₃.With the increase of Nd₆₇Cu₃₃ from 3 wt.%⁹ wt.%,the anisotropy of c axis decreases successively,the orientation degree decreases from 0.814 to 0.208.The appearance of the（Nd,Pr）Cu phase and the increasing of the grain boundary after adding the Nd₆₇Cu₃₃ are the main reasons for the improvement of the coercive force.After the adding of the ally Nd₆₇Cu₃₃,the wettability of the grain boundary increases and then the grains arrange scattered,and the stress between the grains increases and then the die-upseting progress is prevented.The result is that theequiaxed grains increase and the number of lamellar structure decreases.The（004）,（008）peaks appear and the（004）peak is the highest peak for the 6 wt.%Nd₆₇Cu₃₃/94 wt.%Nd_10.5Pr_2.5Fe₈₀Nb₁B₆die-upset after the deformation temperature increases from 1143 K to 1153 K.The orientation degree increases at the same time.The diffusion of the Nd₆₇Cu₃₃ become faster after improving the temperature.The holes of the die-upset decreases significantly and the lamellar structure appears,then the deformation area increases.The factors and mechanism of coercive force of Nd_10.5Pr_2.5Fe₈₀Nb₁B₆ die-upset magnets were studied.As α decreases from 26.0 ° to 9.1 °,the coercive force climbed first from 1346 kA·m-1 to1499 kA·m-1,and then reduces to 1216 kA·m-1.The reason for the increasing of coercive force is own to the contribution of the raising volume fraction of grains break into much smaller grains in size and the increasing of the equiaxed grains.The reasons of reducing coercive force are for more lamellar grains to be obtained,the grain size to be increased and the decreasing of the proportion of the single-domain in magnets,which are the coefficients for the coercive force.The influence of mass fraction content of Nd₆₇Cu₃₃ to the coercive force of Nd₆₇Cu₃₃/Nd_10.5Pr_2.5Fe₈₀Nb₁B₆ die-upset magnets were studied.When the mass fraction content of Nd₆₇Cu₃₃ increases from 3 wt.%⁹ wt.%,the remanence and the maximum magnetic energy reduce from 0.668⁰.637 T and 78.6⁷2.45 kJ·m-3,respectively.The coercive force increases from1395¹609 kA·m-1.The magnet gets the highest coercive force when the mass fraction content of Nd₆₇Cu₃₃ reaches 9 wt.% and the coercive force is 1609 kA·m-1.After adding the Nd₆₇Cu₃₃,the grain boundary of the magnets are thickened,and the grain boundary phase become more non-magnetic,which can hinder the propagation of reversed domains and promote a magnetic isolation of the hard grains.Meanwhile,the presence of such an intergranular phase is considered to improve the wetting behavior of Rich-Rare-Earth phase,and the excess grain boundary phase also causes the smoothing of the interface,removing the local demagnetization field,which also causes a strong pinning effect against the domain wall motion,then the coercivity can be improved.After optimizing the die-upset technology,the coercive force decreases from 1528 kA·m-1 to 1466kA·m-1when the deformation temperature increases from 1143 K to 1153 K.This phenomenon is related to the increasing number of large grains and lamellar structures.So it is better to reduce the temperature when prepare better coercive force of Nd₆₇Cu₃₃/Nd_10.5Pr_2.5Fe₈₀Nb₁B₆ magnets.