Synthesis of high-performance magnetostrictive Tb0.3Dy0.7Fe2 by unidirectional solidification in microgravity

Giant magnetostrictive materials, Tb(0.297)Dy(0.679)Fe(2), were synthesized by unidirectional solidification of a mixture of Tb(0.99)Fe(2) and Dy(0.97)Fe(2) alloys in microgravity with magnetic field of 0-0.12 T. Tb(0.297)Dy(0.679)Fe(2) is a mixed crystal of TbFe(2) and DyFe(2). Tb(0.297)Dy(0.679)Fe(2) synthesized in microgravity with no magnetic field had sheet dendrites structure with 300 (cooling direction) x 200 x 30 microm (thickness) and Fe-rich layer between the sheet dendrites, and they exhibited a tendency for crystalline orientation of <110> and <111> with the cooling direction. The magnetostriction with the cooling direction was 9000 ppm at an external magnetic field of 120 mT. In contrast, Tb(0.297)Dy(0.679)Fe(2) synthesized by unidirectional solidification in normal gravity with no magnetic field had a dendrite structure with a 30-mum diameter x 250-microm length growing in the cooling direction and no preferred orientation. The magnetostriction along the cooling direction was 2000 ppm at an external magnetic field of 120 mT. 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 magnetic field. Examination of the solidification in normal gravity with magnetic field indicated that Tb(0.297)Dy(0.679)Fe(2) 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.