Microstructure and electrochemical properties of rapidly solidified alloy Ml(NiCoMnTi)5

The microstructure and electrochemical properties of MlNi3.7Co0.75Mn0.5Ti0.05 alloys prepared by both rapid solidification and conventional cast methods were comparatively investigated. SEM and XRD studies showed that the microstructure of conventional cast alloy cooled slowly from its melt was of dendrite, where obvious segregation of Mn and trace second phase TiNi3 were found. However, the rapidly solidified alloy (cooling at a rate of about 106 K s−1) was found to be in columnar structure, and contained CaCu5 type single phase only, Mn segregation was restrained effectively as well. Electrochemical measurements showed that the rapidly solidified alloy had higher discharge capacity, more flat discharge potential plateau and longer cycle life than conventional cast alloy, but its activation process was longer. The improved cyclic stability of rapidly solidified alloy was attributed to its composition homogeneity and the fine columnar structure, which showed a good resistance to pulverization and corrosion during charging/discharging cycles.