Effect of cooling rate on the microstructure and hydrogen storage properties of TiFe with 4 wt% Zr as an additive

In this paper, we report the effect of cooling rate on the microstructure and hydrogenation behaviour of TiFe alloy with 4 wt% Zr as an additive. An ingot of TiFe +4 wt% Zr was synthesized by induction melting, using industrial grade Fe and Ti. Step mold with a thickness of 25, 13, 6 and 3 mm were used to obtain different cooling rates. It was found that higher cooling rate leads to a rapid solidification and finer distribution of the secondary phase. There was no effect of cooling rate on the chemical composition of the different phases present in all thicknesses. However, faster cooling rate leads to faster first hydrogenation kinetics. The reason is that the scale of the secondary phase decreases with increasing cooling rates. The decrease in the scale of the secondary phase was evidenced by the measure of its perimeter. During activation, the hydrogenation rate limiting step for all alloys was found to be 3D growth, diffusion controlled with decreasing interface velocity. The gateway mechanism for the enhanced first hydrogenation kinetics has been confirmed.