Abstract: Nb₃₀Hf₃₅Ni_35–xCo_x (x = 0, 5, · · · , 35) alloys were prepared through tungsten arc-melting. The composition and structure of the alloys was analyzed with scanning electron microscope (SEM) and X-ray diffraction (XRD). Evolution of as-cast structures with the Co content was studied. Hydrogen permeation experiments were conducted at various temperatures and pressure differentials. Relationship between hydrogen permeability and composition of Nb-Hf-Ni (Co) alloys was built. It has been shown that, as the Co content increases, the content of impurities of intermetallic phase in the alloy and volume fraction of the primary bcc-Nb phase gradually reduce, while volume fraction of the bcc-Nb in the eutectic gradually increases. Eutectic morphology changes from rods to lamellas. Hydrogen permeability of the alloys increases with increasing Co content.

Key words: hydrogen permeation, microstructure, Nb-Hf-Ni-Co alloy