Ultra-fine grained Nd-Fe-B by high pressure reactive milling and desorption

This paper reports on the grain refinement in dynamic hydrogenation disproportionation desorption and recombination (d-HDDR) processed Nd-rich Nd2Fe14B and stoichiometric Nd2Fe14B powders using high pressure reactive milling (HPRM) followed by a subsequent desorption and recombination. In contrast to the dynamic-HDDR processed anisotropic powder with a grain size of the Nd2Fe14B phase of 300 nm, the new approach yields a further reduction of the Nd2Fe14B1 grain size to less than 70 nm. Nd-rich Nd2Fe14B powder produced by HPRM and subsequent desorption exhibits a coercivity mu H-01(c)=1.35 T and a remanence of 0.80 T. In the stoichiometric material, the reduction of the Nd-content leads to an increase in remanence to 0.85 T. Additionally, it is demonstrated that highly anisotropic powders can also be obtained by dynamic-HDDR processing of stoichiometric Nd2Fe14B powders. (C) 2012 Elsevier B.V. All rights reserved.