It has recently been reported that Nb-Ni-Zr alloys exhibit high hydrogen permeability [1]. The Nb-Ni-Zr alloys have a composite microstructure where a Nb rich bcc phase with high hydrogen permeability is surrounded by structural frameworks of a NiZr+bcc eutectic phase. But their resistance against hydrogen embrittlement is insufficient for an industrial hydrogen production. These hydrogen permeation alloys have been prepared by conventional melting and casting processes and hence, their grain size is in the order of microns. However, the resistance against hydrogen embrittlement could potentially be enhanced if the microstructure of the Nb-Ni-Zr alloys is reduced significantly. Since crystallization of amorphous precursors is known to be effective in realizing nanostructures in some alloy systems, we have investigated the formation range of an amorphous phase in the Nb-Ni-Zr ternary system. In addition, in order to clarify the formation of nanostructures, the decomposition behavior of the amorphous Nb-Ni-Zr alloys has also been investigated by means of differential thermal analysis (DTA) and transmission electron microscopy (TEM).

By using the compositional formula (Nb₉₀Zr₇Ni₃)_1-x (Ni₅₀Zr₅₀)_x, the formation of an amorphous phase by melt-spinning is found for x = 0.5 - 0.9. The formation of a Nb/NiZr nanocomposite was confirmed by TEM after crystallization. The grain size of the nanocomposite (12 nm) is about three orders of magnitude smaller than that of the conventionally prepared Nb-Ni-Zr alloys for hydrogen permeation.

[1] K. Ishikawa, T. Takano, T. Matsuda and K. Aoki, Appl. Phys. Lett., 87 (2005) 081906.