Highly coercive rapidly solidified Sm–Co alloys

Authors

Shampa Aich, University of Nebraska - LincolnFollow
V.K. Ravindran, University of Nebraska - Lincoln
Jeffrey E. Shield, Iowa State UniversityFollow

Date of this Version

4-25-2006

Comments

Published by Am Inst of Physics. J. Appl. Phys. 99, 08B521 2006. Copyright 2006. Permission to use. http://www.aip.org/

Abstract

Highly coercive (H_c up to 37 kOe at 300 K), high remanent permanent magnets have been achieved by rapid solidification of binary Sm–Co alloys and Sm–Co alloys modified with Nb and C. Rapidly solidified SmCo_x alloys with x ranging from 5 to 11.5 formed predominantly a solid solution TbCu7-type SmCo7 phase, although hcp Co was observed for x>7.3. A coercivity value of 10 kOe was observed for xx, as primary dendrites. Additions of 3 at. % Nb or 3 and 5 at. % C profoundly affected the coercivity values. Transmission electron microscopy (TEM) investigations revealed the origin of the improved coercivity. The addition of Nb resulted in a significant reduction in microstructural scale. The SmCo₇ grain size decreased systematically with Nb content, reaching 150–200 nm at 3 at. % Nb. The addition of C also significantly enhanced the coercivity, which systematically increased with C content and reached 37 kOe at 5 at. % C. The effect of C, however, resulted in morphological changes as TEM revealed the formation of an intergranular phase that effectively isolated the hard magnetic SmCo₇ grains from one another, reducing magnetic interactions. Excellent isotropic energy products of 6–8 MGOe were also achieved.