Hydrogen Permeability in Nb–Ti–Ni Alloys Containing Much Primary (Nb,Ti) Phase

Abstract

In order to develop high hydrogen permeability alloys, structural changes induced by hydrogenation, microstructures and hydrogen permeability È were investigated for samples on the straight line connecting the eutectic and the primary phase in the Nb-Ti-Ni phase diagram. È was measurable in the alloys containing much amount of the eutectic phase, indicating that the eutectic microstructure suppresses the hydrogen embrittlement. The value of È increased with increasing Nb content and the volume fraction of the primary (Nb,Ti) phase. The most Nb-rich Nb 68 Ti 17 Ni 15 alloy showed the highest È of 4:91 Â 10 À8 (mol H 2 m À1 s À1 Pa À0:5 ) at 673 K, which is 2.5 times higher than that of the Nb 39 Ti 31 Ni 30 alloy, which has been reported to be highest in the Nb-Ti-Ni alloys. The present work demonstrated that the hydrogen permeable alloys are extended on the straight line connecting the eutectic and the primary phase to the Nb-rich side in the Nb-Ti-Ni system.

Microstructures and hydrogen permeability of directionally solidified Nb–Ni–Ti alloys with the Nb–NiTi eutectic microstructure

“…2(a) and (d)), again indicating the importance of aligning Nb rods so as to penetrate the thickness of the membrane. The largest value of hydrogen permeability obtained at 673 K for the perpendicular configuration specimen grown at 1.0 mm/h is as high as 2.60 Â 10 À8 mol H 2 m À1 s À1 Pa À1/2 , which is more than twice that reported for the as-cast Nbe40Nie40Ti eutectic alloy and is comparable to that reported for the NbeNiTi alloys consisting of grains of the primary Nb phase and those of the eutectic [11]. Of importance to note is that no cracks are observed after hydrogen permeability measurements for all the specimens investigated, indicating that the directionally solidified alloys with the aligned NbeNiTi eutectic microstructure is not susceptible to hydrogen embrittlement at all during hydrogen permeation.…”

Microstructure and hydrogen permeation of cold rolled and annealed Nb40Ti30Ni30 alloy

“…Especially, the alloys indicated by double circles show a higher rolling reduction rate (higher than 80%). We can see that the alloys showing high r u values locate near the line connecting the compositions of Ti 50 Ni 50 and Nb 85 Ti 15 , which corresponds to the line connecting the eutectic and the primary phases [10]. As an example, an XRD pattern of the as-cast Nb 40 Ti 30 Ni 30 alloy, which shows 80% or more rolling reduction rate, is shown in Fig.…”

“…These Nb-TiNi alloys consist of the primary (Nb, Ti) and the eutectic {(Nb, Ti) þ TiNi} phases. It has been reported that the former phase contributes mainly to hydrogen permeation, while the latter one mainly suppresses the hydrogen embrittlement [10,11]. However, it is uncertain whether the thin membrane can be fabricated by rolling and subsequent anneal of these NbTiNi alloys.…”

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

“…On the other hand, it has been reported that hydrogen permeation in the Nb-TiNi alloys is mainly determined by the primary phase. 15) Then, the main reason for the increment of È with increasing Ti/Ni ratio is considered to be the increase of the volume fraction of the primary phase. Chemical compositions of the primary phases vary widely and complicatedly as shown in Table 1, but we can notice the following tendency.…”