Directional annealing studies on rapidly solidified Sm-Co-Nb-C alloys

In this paper, a process that develops texture in nanocrystalline permanent magnet alloys is presented. An originally isotropic material is passed through a high up-temperature gradient, inducing directional grain growth. Texture development by directional annealing of melt-spun Sm12Co88, (Sm12Co88)(99)Nb-1, (Sm12Co88)(99)C-1, and (Sm12Co88)(98)Nb1C1 alloys was examined. Samples directionally annealed were compared with conventionally annealed samples. Strong (006) in-plane texture was observed by X-ray diffraction in Sm12Co88 and (Sm12Co88)(99)Nb-1 alloys and the anisotropy was corroborated by magnetic measurements (magnetic texture similar to 20-53%). Directional annealing produced only slight texture in the (Sm12Co88)(99)C-1 and (Sm12Co88)(98)Nb1C1 alloys. The development of texture is critically dependent on annealing temperature, the up-temperature gradient, translational velocity, and alloy composition. The activation energy for anisotropic grain growth was estimated to be similar to 28 and similar to 42 kJ mol(-1) for Sm12Co88 and (Sm12Co88)(99)Nb-1, respectively. These results indicate that directional annealing as a route to texture development in nanocrystalline permanent magnet alloys is a feasible process. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.