Hydrogen permeability and microstructure of rapidly quenched Nb-TiNi alloys

Research highlights: → Wide and thin Nb-TiNi alloy ribbons were prepared by rapidly quenching technique. → Amorphous phase is partially contained in the Nb30Ti35Ni35 alloy ribbon. → Granular (Nb, Ti) phase precipitates in the TiNi matrix after annealing. → Brittleness in the as-quenched alloy ribbons is recovered by annealing. → Their hydrogen permeability is comparable with that of Pd. - Abstract: Effect of annealing on structure, microstructure and hydrogen permeability of rapidly quenched Nb30Ti35Ni35 and Nb40Ti30Ni30 alloy ribbons were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and the gas flow method. Crystalline (Nb, Ti) and TiNi phases coexisted with the amorphous phases in the as-quenched Nb30Ti35Ni35 alloy, while only crystalline (Nb, Ti) and TiNi phases were formed in the as-quenched Nb40Ti30Ni30 alloy. Both the as-quenched alloys were too brittle to measure their hydrogen permeability, but they became ductile by annealing above 1173 K and showed the microstructure consisting of the crystalline (Nb, Ti) phase embedded in the crystalline TiNi matrix. The volume fraction of the (Nb, Ti) phases in the Nb-TiNi alloys increased with increasing Nb content. Hydrogen permeability at 673 K, i.e. Φ673 K of the crystalline Nb30Ti35Ni35 and Nb40Ti30Ni30 alloys was 1.1 x 10-8 and 1.9 x 10-8 (molH2/m/s/Pa0.5), respectively, which were comparable with that of Pd. The present work has clearly demonstrated that the rapid quenching technique and subsequent annealing process are useful and attractive method for the preparation of hydrogen permeable Nb-TiNi alloy membrane.