Characterization of MmNi3.6Co0.75Mn0.55Al0.1 alloys prepared by casting and quenching techniques

An investigation is made of the effects of the solidification rate on the electrochemical properties and structure of alloys with composition MmNi3.6Co0.75Mn0.55Al0.1. By using the rapid quenching preparation technique, the electrode durability of this hydride-forming compound can be greatly improved at the expense of a small decrease in capacity compared with those of the cast alloy. Rapid quenching can also flatten and raise the discharge voltage plateau to a much more promising level, but rapidly quenched alloys generally show a lower activation speed. The higher the quenching rate, the longer the cycle life, the higher and flatter the discharge voltage plateau, but the lower the capacity. X-ray diffraction patterns and SEM observations indicated that whereas there are segregations in the master alloy, there are none in as-quenched alloys whose crystal grain is much smaller than that of the master alloy.