Study of the solidification microstructure as a function of the cooling rate in Nd-Fe-B alloys for sintered magnets


A solidification experiment with an alloy with composition Nd15Fe77,5B7,5 was performed under argon atmosphere using a vacuum induction furnace, by pouring the liquid metal onto a water-cooled copper chill, aiming at evaluating the effect of the cooling rate on the solidification microstructure. Temperature measurements were conducted throughout the experiment with thermo couples placed at the heights of 1 mm, 7 mm and 31 mm from the chill base. The analysis of the temperature curves and the material’s microstructure showed that the formation of alpha-iron is inhibited only with a relatively super high cooling and, consequently, with high solidification rates, in accordance with the literature. The chemical analysis revealed that the loss of Nd by evaporation is negligible and that most contaminants present are similar to those of commercial alloys, except for Si, which may have originated from the reaction of the liquid metal with the alumina-silica crucible.

SILVEIRA, João Ricardo Filipini da; NAGASIMA, Thiago Pires. Estudo da microestrutura de solidificação em função da taxa de resfriamento de ligas Nd-Fe-B para imãs sinterizados. Revista IPT – Tecnologia e Inovação, v.1, n.6, p.60-77, dez., 2017.

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