Unidirectional Solidification of Laves Phase Intermetallic Compound, Tb0.297Dy0.679Fe2 in Microgravity

Abstract

Giant magnetostrictive materials, Tb0.297Dy0.679Fe2, were synthesized by unidirectional solidification of a mixture of Tb0.99Fe2 and Dy0.97Fe2 alloys in microgravity with magnetic field of 0 to 0.12T. Tb0.297Dy0.679Fe2 is a mixed crystal of TbFe2 and DyFe2. Tb0.297Dy0.679Fe2 synthesized in microgravity with no magnetic field had sheet-dendrites structure with 300 (cooling direction) x 200 x 30µm (thickness) and Fe-rich layer between the sheet-dendrites growing in the cooling direction, and exhibited a tendency for crystalline orientation of ＜110＞ and ＜111＞ with the cooling direction. The magnetostriction with the cooling direction was 9000ppm at an external magnetic field of 120mT. In contrast, Tb0.297Dy0.679Fe2 synthesized by unidirectional solidification in normal gravity with no magnetic field had a dendrite structure with a 30µm diameter x 250µm length growing in the cooling direction and no preferred orientation. The magnetostriction along the cooling direction was 2000ppm at an external magnetic field of 120mT. Analysis of the solidification in microgravity with magnetic field revealed that the dendrites oriented along the cooling direction and that the tendency for crystalline orientation of ＜110＞ and ＜111＞ with the cooling direction increased with increases in the magnetic field. Examination of the solidification in normal gravity with magnetic field indicated that Tb0.297Dy0.679Fe2 consisted of sheet dendrites without orientation and revealed no preferred orientation. The magnetostriction along the cooling direction increased with increases in the magnetic field. The effects of microgravity and magnetic field on the structure and crystalline orientation were considered.