INVESTIGATIONS ON ML(NICOMNTI)(5) ALLOYS PREPARED WITH DIFFERENT SOLIDIFICATION RATES

The influence of the solidification rate on the electrochemical charge /discharge behaviour and structure of the Mischmetal based alloys of t he type ML(NiCoMnTi)(5) was systematically investigated. The cycle sta bility and discharge plateau characteristics of the material could be greatly improved by using a high-rate solidification technique. The cy cle durability increased with the increasing solidification rate, but the capacity, especially the capacity with high discharge rate, decrea sed. High solidification rate also made the activation difficult. X-ra y powder diffraction analysis and scanning electron microscope (SEM) o bservations indicated that alloys with different solidification rates had different degrees of segregation and atomic disorder. Transmission electron microscope (TEM) studies showed that the grain size of the q uenched alloy with a quenching rate of 27 ms(-1) was very small and th at there is coexistence of a nano-crystalline and an amorphous phase. (C) 1998 Elsevier Science S.A.