Design Of Hydrogen Separatinwg Nb-Ti-Fe Membranes With High Permeability And Low Cost

Nowadays, group 5B (Nb-, V-, and Ta-based) alloys are considered prospective candidates to replace commercial Pd-based hydrogen permeation membranes. In recent years, the focus of research efforts towards these metal membranes has been the development of robust/cheaper alloys and the exploration of related phase diagrams. To address this challenge, the phase diagram and solidification path of the Nb-Ti-Fe alloy system have been investigated within the CALPHAD (CALculation of PHAse Diagrams) approach by combining available experimental data. On this basis, Nb-Ti-Fe multi-phase hydrogen-permeable alloys have been designed and fabricated, and their microstructure, hydrogen permeability, and hydrogen embrittlement (HE) resistance were evaluated. The results obtained show four ternary invariant reactions and five phase regions in the liquidus projection, where the compositional region suitable for hydrogen permeation has been established successfully. Small variations in alloy composition (e.g. Nb or Ti/Fe ratios) can lead to large changes in hydrogen permeation properties. This is attributed to the TiFe phase in the eutectic structure transition from a continuous thin layer to discontinuous granules. In particular, Nb5Ti60Fe35 shows the highest permeability at 673 K, 3.82 x 10(-8) mol H-2 m(-1) s(-1) Pa-1/2, which, heretofore, is the highest value reported in this alloy system.