Unidirectional solidification of Tb-Fe giant magnetostrictive alloys under microgravity conditions

Abstract

The crystal growth of Tb-Fe giant magnetostrictive materials under microgravity (μG) and terrestrial gravity (1G) was investigated. The microgravity conditions were obtained by free fall in drop tower facility at the Japan Microgravity Center (JAMIC). TbFe 1.83 alloy with 1 gram and cubic form was prepared for unidirectional solidification under microgravity environment. The samples were melted just before drop and solidified by contact chill against a sample at the period of microgravity after dropping. The microstructure of μG sample was columnar structure and growth direction was aligned in thermal gradient. In 1G sample, the microstructure was weak aligned in thermal gradient. The composition was measured by EDX. The TbFe 3 phase was observed in 1G sample, and no TbFe 3 phase was observed in μG sample, caused by reduction of thermal convection in microgravity environment. In μG sample, the columnar structure that aligned thermal gradient was oriented orientation. The magnetostriction of parallel direction to the thermal gradient was larger than perpendicular direction in μG and 1G. The magnetostriction of μG sample, the measurement direction was parallel to the thermal gradient, was larger than 1G sample caused by microstructure.