Effect of yttrium content on microstructure and hydrogen storage properties of TiFe-based alloy

Abstract

In this paper, the experimental alloy with the standard composition of Ti1.1-xZr0.1YxFe0.6Ni0.3Mn0.2 (x = 0–0.08) was synthesized by vacuum induction melting. The activation properties and hydrogen absorption/desorption kinetics were significantly improved by adding different amounts levels of rare earth elements Y to partially replace Ti in TiFe alloys. The microstructure, phase composition and hydrogen storage properties of the alloy before and after hydrogen absorption/desorption were characterized and tested by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and Sieverts-type manual PCT hydrogen storage tester. The experimental results show that the as-cast alloy consists of Ni-rich TiFe main phase, a small amount of ZrMn2 phase biased on the TiFe phase and Y-rich phase. The addition of Y significantly increases the phase boundary and refines the crystallization, and significantly shortens the activation incubation period of the cast alloy. The alloy requires only the first hydrogen absorption to fully achieve activation at 150 °C, and still exhibits a fast hydrogen absorption rate at −10 °C. Meanwhile, When the Y content is 0.02, the saturation rate (R100a) of hydrogen absorption reaches 92%, and the maximum hydrogen absorption capacity is 1.704 wt% at 70 °C. And the absolute values of the enthalpy and entropy changes of hydrogen absorption/desorption increase with the increasing of Y content.