Abstract
α-Fe/R2Fe14B-type exchange-coupled NdFeB nanocomposites with an intrinsic coercivity, iHc, of 9.5-13.2 kOe and maximum energy product, (BH)max, of 16-19. 8 MGOe have been successfully produced from melt spun ribbons with compositions of (Nd0.95La0.05)10.5-11Febal. Cr2B10 and (Nd0.95La0.05)9.5Fe68Co10Cr2B10.5. It was found that a dilute substitution of La for Nd refines the grains, and a partial substitution of Cr for Fe suppresses the formation of the R2Fe23B3 and Fe3B phases during crystallization and promotes the formation of an α-Fe/R2Fe14B mixture. Unlike the ternary Nd-Fe-B system, La and/or Cr substitution are effective in suppressing the formation of Fe3B and R2Fe23B3 phase in the (Nd0.95La0.05)9.5Fe88.5-xCr2Bx, where x ranged from 6 to 10.5. Both Br and (BH)max decrease initially with increasing boron content, then increase slightly when the boron content was increased above 9. Some of the boron was presumed to react with Cr forming Cr-broides within R2Fe14Band near the grain boundary region. Increasing the total rare earth content in (Nd0.95La0.05)yFe88-yCr2B10 ribbons was found to enhance both the remanence, Br, and the iHc of ribbons simultaneously. A Br of 9.2 to 9.5 kG, iHc of 11.1 to 13.2 kOe and (BH)max of 16.5 to 18.0 MGOe have been obtained on (Nd0.95La0.05)10.5-11Febal.Cr2B10. Significant increases in Br and (BH)max values were obtained in (Nd0.95La0.05)9.5Fe78-zCozCr2B10.5 when z is varied from 7.5 to 10. Microstructural change may play a critical role in explaining the high Br, BHmax and iHc values obtained on (Nd0.95La0.05)9.5Fe68Co10Cr2B10.5.
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