Study on the microstructure and hydrogen storage property changes of cast TiFe0.9Cr0.1 alloy by homogenization annealing

Abstract

This study investigated the changes in the microstructure and hydrogen storage properties of cast TiFe0.9Cr0.1 alloys by homogenization annealing. The as-cast and homogenized samples consisted of B2 and C14 Laves phase. After annealing, compositions of the B2 phase in both samples were similar, while the Laves phase fraction decreased and the Cr concentration in the Laves phase increased. To understand the microstructure changes caused by annealing, the fraction and the composition of the phases in the equilibrium state were derived using thermodynamic calculation, where the microstructure of the as-cast sample changed to the direction in the equilibrium state by annealing. The first hydrogenation kinetics were examined in the as-cast and homogenized samples, which slowed in the latter as the Laves phase fraction decreased. The hydrogen absorption and desorption behaviors were compared using a pressure-composition-temperature diagram at 50 °C. Since the compositions of the B2 phase in the two samples were almost the same, the two samples represented similar hydrogen storage behaviors. From the first-principles density functional theory calculation, the hydride-forming enthalpy of the B2 phase was calculated. By using an equation to predict the desorption plateau pressure from the hydride-forming enthalpy, the desorption pressure was predicted to be 1.34 bar, a value similar to the desorption pressure obtained from the experiment.