STUDY ON REPRODUCIBILITY OF MAGNETIC PROPERTIES OF HDDR-TREATED Nd-Fe-B-TYPE MATERIAL

Abstract

One of the most effective ways to manufacture a high performance Nd-Fe-B permanent magnet powder is the HDDR process. However, there are some practical problems yet to be solved, such as lack of reproducibility of coercivity and residual hydrogen, and so on. Improving the reproducibility of magnetic properties of Nd-Fe-B-type powder prepared by HDDR treatment is important in practical point of view. In this study, reproducibility of coercivity of the HDDR-treated Nd-Fe-B-type material was examined. It was found that additional de-gassing treatment was beneficial for improving the reproducibility of coercivity. The additional de-gassing caused further lattice shrinkage of the Nd2Fe14B matrix phase, hence causing more micro-cracks in the matrix phase. Micro-cracks in the material facilitated the hydrogen diffusion, and improved homogeneity of the HDDR reactions. The improved homogeneity of the HDDR reactions led to an improved reproducibility of coercivity of HDDR-treated Nd-Fe-B material.