Microstructural evaluation of Nd-Fe-B jet-milled powders

Abstract

Nd-Fe-B sintered magnets have high energy products and are used for various applications. Motors of hybrid vehicles (HEVs) are one of the major applications. For usage of HEVs, Dy is added to Nd-Fe-B magnets to maintain coercivity at high temperature environment. However, due to low natural resources of Dy, Dy-free or Dy-lean Nd-Fe-B sintered magnets are strongly required. To achieve high coercivity, it is necessary that microstructure of sintered magnets is consisted of both fine main phase particles and homogeneously distributed Nd-rich phases around the main phase. In this study, the microstructure of Nd-Fe-B jet-milled powders and the distribution of the Nd-rich phase were investigated. The distribution of the Nd-rich phase was evaluated by the ratio of grains which contain the Nd-rich phase. With decreasing size of the jet-milled Nd-Fe-B powder, the Nd-rich phase tends to aggregate and its distribution becomes inhomogeneous. The powder size of Nd-Fe-B jet-milled powder is much smaller than the average lamella interval of strip cast alloys. © 2009 The Japan Institute of Metals.