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

Abstract

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 300nm, the new approach yields a further reduction of the Nd2Fe14B1 grain size to less than 70nm. Nd-rich Nd2Fe14B powder produced by HPRM and subsequent desorption exhibits a coercivity μ0iHc=1.35T and a remanence of 0.80T. In the stoichiometric material, the reduction of the Nd-content leads to an increase in remanence to 0.85T. Additionally, it is demonstrated that highly anisotropic powders can also be obtained by dynamic-HDDR processing of stoichiometric Nd2Fe14B powders.