Microstructures and Hydrogen Permeability of Nb-Ti-Ni Alloys with High Resistance to Hydrogen Embrittlement

Abstract

Microstructures and hydrogen permeability (È) of as-cast Nb-Ti-Ni alloys have been investigated by scanning electron microscopy (SEM) and by the gas permeation technique, respectively. The È value increases with increasing temperature and the amount of the Nb content for every alloy. In these alloys, the Nb 39 Ti 31 Ni 30 alloy, consisting of the primary bcc-(Nb, Ti) solid solution and the eutectic {(Nb, Ti)+TiNi} phase, shows the highest È, which is equivalent to that of Pd. On the other hand, the Nb 10 Ti 50 Ni 40 alloy, consisting of the primary B2-TiNi compound and the eutectic {(Nb, Ti)+TiNi} phase, shows the lowest È value among the alloys for which È is measurable. Eutectic microstructures suppress the hydrogen embrittlement, while the primary (Nb, Ti) phase contributes to the hydrogen permeation in these alloys. The present work demonstrates that duplex alloys containing eutectic microstructures are promising for hydrogen permeation membranes with high resistance to the hydrogen embrittlement.

Electron Microscopy Study of Eutectic Structure in Nb-Ti-X and Nb-Zr-X (X = Co, Ni) Hydrogen Permeation Alloys

“…The hydrogen permeability of the Nb-Ti-Ni alloy increases with the volume fraction of the primary (Nb, Ti) phase. 4,5) On the other hand, the Nb-Ti-Co alloy with the eutectic composition possesses the highest hydrogen permeability among all the Nb-Ti-Co ternary alloys. 6) This indicates that hydrogen permeability depends on the alloy systems and their compositions.…”

“…Recently, one of the authors found out that the Nb-Ti-Ni alloy consists of bcc-(Nb, Ti) + B2-TiNi eutectic microstructures with an appropriate combination of high-hydrogen permeability and excellent hydrogen embrittlement resistance. 4,5) The former property is attributable to the bcc-(Nb, Ti) phase, while the latter property is attributable to the B2-TiNi phase in the eutectic structure. On the basis of the same concept, Nb-Ti-Co, 6) Nb-Zr-Ni 7,8) and Nb-Zr-Co alloys have been developed as new hydrogen permeation materials.…”

Microstructure, Ductility and Hydrogen Permeability of Nb-Ti-Zr-Ni Alloys

“…The experimental procedure has been described in detail elsewhere. 10,11) 3. Results and Discussion Figure 1 shows the temperature dependence of hydrogen permeability È for the as-cast Nb 40 Ti x Zr 12 Ni 48Àx alloys (x ¼ 14, 18, 20, 22 and 24) in the form of an Arrhenius plot.…”

“…Some groups have tried to develop new alloys such as V-based alloys, 3,4) Nb-based alloys, 5,6) amorphous Zr-Ni alloys, 7) amorphous Zr-Ni-Nb alloys, 8,9) and so on. 10,11) However, the overcoming of the hydrogen embrittlement in these alloys is insufficient. Recently, the present authors have developed new non-Pd based hydrogen permeation alloys such as the Nb-TiNi, 10) the Nb-TiCo 11) and the Nb-ZrNi ones.…”

“…Recently, the present authors have developed new non-Pd based hydrogen permeation alloys such as the Nb-TiNi, 10) the Nb-TiCo 11) and the Nb-ZrNi ones. 12,13) The Nb-TiNi alloys show high È and large ductility, while the Nb-ZrNi ones do higher È and poorer ductility than those of the Nb-TiNi ones, 10,12,13) which are attributed to that the TiNi phase shows larger ductility than that of the ZrNi one, but the latter does higher È than that of the former. In the hydrogen permeation alloys, not only high È, but also some ductility is necessary, because the alloy membrane is mechanically sealed with the gaskets.…”