Effect of high abundance rare earth additions on the thermal diffusion process of NdFeB
The effect of different(Ce,La)contents for high abundance rare earth permanent magnets on thermal dif-fusion have been investigated.The samples compositions were((La,Ce)0.2(Pr,Nd)0.8)FebalB and((La,Ce)0.5(Pr,Nd)0.5)FebalB,respectively.The thermal diffusing behaviors of heavy rare earth Dy were discussed.The results showed that the content of(Ce,La)has a significant influence on the thermal diffusion effect.With the increase of(Ce,La)content,the diffusion effect deteriorated.The analysis of the microstructure and element distribution re-vealed that Dy diffused into the magnet along the grain boundary,and the Dy element in the grain boundary also en-tered the mainphase grains,forming a(Dy,RE)2Fe14B shell layer at its edge during the thermal diffusion process.At the same time,the distribution of RE-rich phases at the grain boundary was optimized,weakening the exchange coupling between the main phase grains and improving the coercivity.High(Ce,La)content would lead to an in-crease in the O content of the magnet,resulting in more oxides in the grain boundary.The lack of coordination with rare earth-rich phases leaded to poor diffusion channels for the Dy thermal diffusion,resulting into inferior distribu-tion of the thin Dy-rich shell layer in the main phase grain.Therefore,the performance improvement is not significant.Based on Fick's second law,the diffusion coefficient of Dy element was calculated.It can be indicated that the content of(Ce,La)has a significant effect on the rate of thermal diffusion.The diffusion coefficients from the surface layer to the center of(Ce,La)20 and(Ce,La)50 magnets were 2.37 × 10-8 and 5.70×10-9 cm2/s,respectively.The diffusion coef-ficients from grain boundaries to the interior of the grains were 1.30× 10-14 and 3.92 × 10-14 cm2/s,respectively.
high abundance rare earth permanent magnetscoerciondiffusion coefficientthermal diffusion process
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