A correlation between intrinsic coercivity-electrical conductivity- thermal treatment in a Nd sub 11.9 MM sub 2.9 Fe sub 73.9 Co sub 3.3 Ni sub 1.1 B sub 6.9 - type magnet

• Published in: Journal of alloys and compounds Vol. 314; no. 1-2; pp. 251 - 256
• Main Authors: Madaah-Hosseini, H R, Kianvash, A, Yoozbashi-Zadeh, H, Seyyed-Reihani, M
• Format: Journal Article
• Language: English
• Published: 16-01-2001
• ISSN: 0925-8388

In this work, the effects of sintering temperature, cooling rate after sintering and post-sintering annealing treatments on the microstructure and magnetic properties of a Nd sub 11.9 MM sub 2.9 Fe sub 73.9 Co sub 3.3 Ni sub 1.1 B sub 6.9 -type magnet have been investigated. It was found that the best magnetic properties were only obtained at a narrow range of sintering temperature at 1333-1353 K. Porosity was found to be minimized with increasing sintering temperature up to 1333 K. However, some grain growth occurred by increasing the sintering temperature from 1333 to 1353 K. Further increase of sintering temperature resulted in a significant decrease in the magnetic properties due to appearance of alpha -iron in the microstructure of the magnets and/or grain growth. The dependence of intrinsic coercivity (H sub cJ ) on the cooling rate (after sintering) and post-sintering annealing treatments has been related to electrical conductivity (EC) of the magnets; thus an increase in the EC resulted in a significant improvement in the H sub cJ values. This could be due to reduction of residual stresses within the specimens during slow cooling after sintering/post-sintering annealing treatments. The compatibility between the variations of the H sub cJ and EC with the cooling rates (after sintering) or a post-sintering annealing treatment at around 873 K confirms this mater.