Effect of microgravity and magnetic field on the metallic and crystalline structure of magnetostrictive SmFe2 synthesized by unidirectional solidification.

The Sm-2Fe molten alloy with 1:2 molar ratio was unidirectionally solidified in both microgravity and normal gravity in concurrence with a magnetic flux (0-0.12 T). The compound SmFe2 was produced by the unidirectional solidification in microgravity with a magnetic flux of 0T and exhibited a lamellar microstructure. The average lamellar thickness was 30 mum and each lamella possessed a <111> crystallographic alignment along major axis aligned in the direction of cooling. Unidirectional solidification in microgravity with a magnetic field of 0.04 T produced crystalline SmFe2 and Fe phases. The microstructure of this product was lamellar with an average lamellar thickness of 17 mum and no crystalline alignment. Unidirectional solidification in microgravity with a magnetic flux ranging from 0.06 to 0.12 T and in normal gravity with a magnetic flux ranging from 0 to 0.12 T produced crystalline Sm2Fe17 and Fe. During unidirectional solidification in microgravity without a magnetic flux, few nucleation sites were formed and rapid crystal growth occurred, consequently forming large-grain SmFe2. The produced SmFe2 had a lamellar structure with a dominant <111> crystallographic alignment in the direction of cooling. Convection in the molten state and where a magnetic flux was present caused homogeneous nucleation, forming Sm2Fe17 with a disordered structure and crystalline alignment coinciding with the formation of the dendritic Fe.