Alloying Effects on the Phase Stability of Hydrides Formed in Vanadium Alloys

Abstract

The alloying effects on the stability of vanadium hydrides have been investigated systematically for binary V-M and ternary V-Ti-M alloys, where M's are various alloying elements. The PCT curves for the β phase (V 2 H or VH) are measured at low hydrogen pressures using an electrochemical method. On the other hand, for the y phase (VH 2 ), the PCT curves are measured at high hydrogen pressures using an ordinary Sieverts-type apparatus. It is found that the phase stability of vanadium hydrides is affected strongly by the presence of a small amount of elements added to vanadium metal. The alloying effects on the hydride stability are different between the y phase and the β phase. For example, the y phase becomes most unstable when the group 8 elements in the periodic table, Fe, Ru and Os, are added to vanadium metal. On the other hand, the stability of the β phase changes monotonously following the order of elements in the periodic table. Also, the efficiency of alloying element in modifying the hydride stability is found to be different between the β 1 phase (V 2 H) and the β 2 phase (VH). In addition, it is shown that the logarithm of the plateau pressures for the β 1 and the γ phases change almost linearly with the amount of alloying element in the alloy. Using this linear relationship for the y phase, the second plateau pressures of ternary V-Ti-Ru and V-Ti-Cr alloys can be estimated quantitatively in the wide compositional range.