Effects of Si addition on the microstructure and the hydrogen storage properties of Ti26.5V45Fe8.5Cr20Ce0.5 BCC solid solution alloys

The microstructure and the hydrogen storage properties of Ti_26.5(V_0.45Fe_0.085)_100−xCr₂₀Ce_0.5Si_x (x = 0 and 1) have been investigated by EPMA, XRD, in situ temperature XRD, neutron diffraction and P-C isotherm. Si addition results in the precipitation of a TiFe₂-type Laves phase and produces chemical heterogeneity in the BCC phase. As a consequence, Si-added alloy exhibits a lower hydrogen capacity and both a higher plateau pressure and slope factor as compared to Si-free alloy. Si enters in both Laves and BCC phases with a higher preference for the former phase. For both alloys, all metal atoms (Ti, V, Fe and Cr) are supposed to be randomly distributed in the 2a sites of the BCC phase and deuterium atoms occupy the 8c sites on fully charged deuterides. Si has no significant influence on the hydrogen occupation. Two hydrides are observed during the desorption process for Ti_26.5(V_0.45Fe_0.085)₁₀₀Cr₂₀Ce_0.5 alloy, a hydrogen rich one with distorted FCC structure (space group: P4/mmm) and a hydrogen poor one with BCT structure (space group: I4/mmm).