MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Detection of Neodymium-Rich Phase for Development of Coercivity in Neodymium-Iron-Boron-Based Alloys with Submicron-Sized Grains Using Positron Lifetime Spectroscopy
Takeshi NishiuchiMasaki NakamuraSatoshi HirosawaMasataka MizunoHideki ArakiYasuharu Shirai
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2010 Volume 51 Issue 3 Pages 535-541

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Abstract

In order to evaluate the relationship between positron lifetime and microstructure, which contributes to the development of coercivity in hydrogenation-disproportionation-desorption-recombination (HDDR)-processed Nd-Fe-B-based alloys, detailed studies of positron lifetime spectroscopy were performed on HDDR-processed Nd-Fe-B-based alloys during desorption-recombination (DR) treatment. After the onset of coercivity, the change in positron lifetime closely corresponded to the change in intrinsic coercivity (HcJ) with the progress of DR treatment. This result can be explained in terms of the grain size of the recombined Nd2Fe14B phases and the diffusion length of positrons, which annihilate in the matrix before reaching the grain boundary. Furthermore, positron lifetime spectroscopy was able to detect small changes in the grain boundary region very sensitively compared with thermal desorption spectroscopy (TDS) and X-ray diffraction (XRD). These changes in the grain boundary region caused the onset of coercivity attributed to the formation of Nd-rich intergranular phases. These results indicate that formation of a small amount of the Nd-rich intergranular phase during the DR process, which could be detected by positron lifetime spectroscopy, contributes to the onset of coercivity, even if NdHx phases remain.

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© 2010 The Japan Institute of Metals and Materials
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