Improvement in high-rate dischargeability, activation, and low-temperature performance in multi-phase AB2 alloys by partial substitution of Zr with Y

Abstract

The changes in structure, gaseous phase hydrogen storage, and electrochemical properties due to the incorporation of Y in the alloy formula have been studied on two series of AB2 alloys, with an originally C14- (relatively higher Cr-content) and a C15- (relatively higher Co-content) predominated microstructure, respectively. In each series, 1–4 at.% of Y was added to the designed formula and partially replaced Zr. A majority of the added Y went into the secondary phases, such as YNi, (Y, Sn)-rich, and Y2O3, and only a small amount being found in the main AB2 phase. The lattice constants and the unit cell volume decreased due to the reduction in Zr-content. The C15 phase abundances of the Y-containing alloys were higher than those of the Y-free alloys in both series. As the Y-content increased, the gaseous phase hydrogen storage capacity measured at 30 °C decreased in the high-Cr series and increased in the high-Co series. Both the hydrogen mid-point pressures and the electrochemical discharge capacities of the Y-containing alloys were lower than those in the Y-free alloys in both series. Both the activation and high-rate dischargeability (HRD) improved with the increase in Y-content. The −40 °C resistance was substantially reduced with the incorporation of Y in both series.