Effect of the disproportionation and recombination stages of the HDDR process on the inducement of anisotropy in Nd–Fe–B magnets

Autor: S. Sugimoto, Motofumi Homma, Masuo Okada, H. Nakamura, Toshio Kagotani, K. Kato, David Book
Rok vydání: 1999
Předmět:
Zdroj: Journal of Alloys and Compounds. :862-867
ISSN: 0925-8388
Popis: The magnetic properties of HDDR (hydrogenation disproportionation desorption recombination) treated Nd 12.2 Fe 81.8 B 6.0 alloys were investigated. Two different patterns were used for the disproportionation stage: (i) the alloys were heated to a certain processing temperature between 850–950°C in 0.1 MPa of hydrogen (conventional hydrogen treatment: c - HD treatment), and (ii) the alloys were heated under vacuum and hydrogen was only admitted when the processing temperature had been reached ( ν - HD treatment). The alloys were then held at the processing temperature for 1 or 2 h under hydrogen in order to cause complete disproportionation. Either an argon heat treatment, or a hydrogen heat treatment at various constant pressures below 0.1 MPa, was then used to control the hydrogen pressure during the recombination stage ( s - DR treatment), followed by the usual heat treatment in vacuum (conventional heat treatment in vacuum: c - DR treatment) to cause complete recombination. It was found that the magnetic properties of the ν -HD powders were more sensitive to the s -DR treatment time than those of the c -HD powders, which is thought to be related to differences in microstructure observed in the disproportionated state. The best magnetic properties were obtained for a ν -HD powder s -DR treated at 950°C for 20 min: B r =1.4 T, j H c =385 kAm −1 , B r / J s =0.92. It can be said that the inducement of anisotropy is influenced by the hydrogenation and desorption stages of the HDDR process, and that the combination of ν -HD and s -DR treatment can be an effective method of inducing anisotropy in Nd–Fe–B powders.
Databáze: OpenAIRE