Preparation and electrochemical properties of unidirectionally solidified Ml(NiCoMnTi) 5 alloys

Abstract

Mischmetal based alloy Ml(NiCoMnTi) 5 (Ml: La-rich mischmetal) was prepared by unidirectional solidification process at an ultra-high temperature gradient (around 1300 °C cm −1) and different growth rates (48∼220 μm s −1). The microstructures and electrochemical properties of these alloys have been investigated. It was shown that with increasing growth rate, the microstructure of unidirectional solidification alloy changed from cellular–columnar to columnar–dendritic structure and the primary columnar spacing λ 1 increased, reached a maximum value and then decreased. Electrochemical measurement indicated that unidirectional solidification alloy with the fine cellular–columnar structure prepared at growth rate R=48 μm s −1 has significantly improved discharge capacity, high-rate dischargeability and cycling stability of the alloy.